Patent Publication Number: US-9423216-B2

Title: KeyMod quick mounting arrangement

Description:
CROSS REFERENCE OF RELATED APPLICATION 
     This is a Continuation-In-Part application that claims the benefit of priority under 35 U.S.C. §119 to a non-provisional application, application Ser. No. 14/218,893, filed Mar. 18, 2014, now U.S. Pat. No. 9,341,441. 
    
    
     NOTICE OF COPYRIGHT 
     A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to any reproduction by anyone of the patent disclosure, as it appears in the United States Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND OF THE PRESENT INVENTION 
     1. Field of Invention 
     The present invention relates to a firearm accessory attachment system of a firearm, and more particular to a KeyMod quick mounting arrangement, which provides a quick and precise attachment for a firearm accessory to be detachably mounted at the firearm. 
     2. Description of Related Arts 
     Conventional accessory mounts, such as “Picatinny rail system or “Weaver” rail system, have evolved in the firearm industry from a military standard. The conventional accessory mount generally provides a rail comprising a plurality of T-shaped cross sectional raised ridges formed at the firearm, and an adapter provided at the accessory, wherein the accessory can be mounted at the rail by transversely sliding the adapter at the rail and fastening the adapter at the rail via a bolt. However, the conventional accessory mount has several drawbacks. The rail will only enable the accessory to be mounted at the firearm at the transverse direction. It is not ergonomic for a user to hold the firearm and mount the accessory to the rail in a transverse direction to the discharge axis of the firearm. In addition, the rail profile with the raised ridges will substantially increase the overall weight of the firearm. More importantly, the rail cannot provide a quick and precise attachment for the firearm because the adapter must be fastened with the rail by the bolt. 
     A “KeyMod” mounting arrangement is an improved system superior to the conventional accessory mount. The KeyMod mounting arrangement generally comprises a plurality of KeyMod mounting slots provided at the firearm and a KeyMod mounting nut provided at the accessory. In particular, each of the mounting slots, which is extended along the discharge axis of the firearm, has a keyhole configuration defining an enlarged slot portion with larger diameter and a narrower slot portion extended therefrom, wherein the slot is chamfered on the backside. Therefore, the mounting nut can be disposed in the enlarged slot portion and slid to the narrower slot portion. Then, the mounting nut can be fastened at the narrower slot portion by a bolt to lift the mounting nut at the backside of the mounting slot in order to secure the accessory at the firearm. The KeyMod mounting arrangement can solve the existing problems by providing an ergonomic mounting way to mount the accessory at the firearm corresponding to the discharge axis thereof, and by substantially reducing the overall weight of the firearm incorporating with the KeyMod mounting slots. However, the KeyMod mounting arrangement has several drawbacks. 
     The alignment between the mounting nut and the enlarged slot portion of the mounting slot must be precise. Especially when two or more mounting nuts are provided at the accessory, the user must correctly align the mounting nuts with the enlarged slot portions of the mounting slots respectively. Since the mounting nuts are movable, the user must hold the mounting nuts stationary before the mounting nuts are plugged into the enlarged slot portions of the mounting slots. It is worth mentioning that the mounting nuts can only be stationary or locked after the mounting nuts are lifted by the bolts to couple at the narrower slot portions of the mounting slots. In other words, the KeyMod mounting arrangement provides a displeasing mounting operation comparing with the conventional “Picatinny rail system or “Weaver” rail system. Furthermore, the KeyMod mounting arrangement still cannot provide a quick and precise attachment for the firearm because the mounting nut must be fastened with the mounting slot by the bolt. 
     SUMMARY OF THE PRESENT INVENTION 
     The invention is advantageous in that it provides a KeyMod quick mounting arrangement, which provides a quick and precise attachment for a firearm accessory to be detachably mounted at the firearm. 
     Another advantage of the invention is to a KeyMod quick mounting arrangement, which can incorporate an existing KeyMod slot rail to mount the accessory, such as laser module, scope mount, flashlight module, navigation light module, camera module, vertical grip, rail panel, hand stop, barricade support, at the firearm. In other words, the KeyMod quick mounting arrangement does not require to alter the original structural design of the KeyMod mounting structure of the firearm, so as to minimize the manufacturing cost of the KeyMod mounting structure of the firearm incorporating with the KeyMod quick mounting arrangement. 
     Another advantage of the invention is to a KeyMod quick mounting arrangement, which comprises a coupling head being slid and lifted in one single action to secure the accessory at the firearm. 
     Another advantage of the invention is to a KeyMod quick mounting arrangement, wherein the coupling head is stationary and locked in a releasing position and in a securing position, such that the coupling head can be precisely and rapidly plugged into the enlarged slot portion of the KeyMod slot to enhance the mounting operation of the accessory at the firearm. 
     Another advantage of the invention is to a KeyMod quick mounting arrangement, which comprises at least one positioning member arranged to engage with a second KeyMod slot adjacent to the KeyMod slot where the coupling head is coupled thereat, so as to ensure the corrected alignment between the accessory and the firearm and to prevent any unwanted longitudinal and/or rotational movement of the accessory with respect to the firearm after the KeyMod quick mounting arrangement is mounted to the firearm. 
     Another advantage of the invention is to a KeyMod quick mounting arrangement, wherein the user does not require any tool to fasten and secure the coupling head at the mounting slot, such that the KeyMod quick mounting arrangement provides a tool-less mounting system to speed up the mounting operation of the accessory at the firearm. 
     Another advantage of the invention is to provide a KeyMod quick mounting arrangement, wherein no expensive or complicated structure is required to employ in the present invention in order to achieve the above mentioned objects. Therefore, the present invention successfully provides an economic and efficient solution for providing a secure and reliable configuration for detachably mounting the accessory at the firearm with compact and ergonomic design. 
     Additional advantages and features of the invention will become apparent from the description which follows, and may be realized by means of the instrumentalities and combinations particular point out in the appended claims. 
     According to the present invention, the foregoing and other objects and advantages are attained by a KeyMod quick mounting arrangement for detachably coupling an accessory at a firearm having one or more KeyMod mounting slots, comprising: 
     a mounting body having a first side adapted for extending from the accessory to be detachably coupled with the firearm, and an opposed second side; 
     a positioning unit which comprises a positioning member protruded from the second side of the mounting body for detachably engaging with a narrow slot portion of the mounting slot; and 
     a coupling head, which is movably extended from the mounting body between a releasing position and a securing position, having a head portion outwardly protruded from the second side of the mounting body, wherein in the securing position, the head portion of the coupling head is arranged for being disposed in an enlarged slot portion of the mounting slot so as to secure the accessory at the firearm, and in the releasing position, the head portion of the coupling head is arranged for disengaging with the enlarged slot portion of the mounting slot so as to enable the accessory to be detached from the firearm. 
     In accordance with another aspect of the invention, the present invention comprises a KeyMod quick mounting arrangement for detachably coupling an accessory at a firearm having one or more KeyMod mounting slots, comprising: 
     a mounting body having a first side adapted for extending from the accessory to be detachably coupled with the firearm, and an opposed second side; and 
     a coupling head, which is movably extended from the mounting body between a releasing position and a securing position, having a head portion outwardly protruded from the second side of the mounting body, wherein the mounting body is stationary when the coupling head is moved between the releasing position and the securing position, wherein in the releasing position, the head portion of the coupling head is arranged for being disposed in an enlarged slot portion of the mounting slot, and in the securing position, the head portion of the coupling head is arranged for being slid to a narrower slot portion of the mounting slot for securing the accessory at the firearm. 
     In accordance with another aspect of the invention, the present invention comprises a KeyMod quick mounting arrangement, for detachably coupling an accessory at a firearm having one or more KeyMod mounting slots, comprising: 
     a mounting body having a first side adapted for extending from the accessory to be detachably coupled with the firearm, and an opposed second side; 
     a coupling head, which is movably extended from the mounting body between a releasing position and a securing position, having a head portion outwardly protruded from the second side of the mounting body; and 
     an actuating member movably coupled at the mounting body to move the coupling head between the releasing position and the securing position, wherein in the releasing position, the head portion of the coupling head is arranged for being disposed in an enlarged slot portion of the mounting slot, and in the securing position, the head portion of the coupling head is arranged for being slid to a narrower slot portion of the mounting slot and for being moved toward the second side of the mounting head at the same time for securing the accessory at the firearm. 
     In accordance with another aspect of the invention, the present invention comprises a KeyMod quick mounting arrangement, for detachably coupling an accessory at a firearm having one or more KeyMod mounting slots, comprising: 
     a mounting body having a first side adapted for extending from the accessory to be detachably coupled with the firearm, and an opposed second side; 
     a coupling head, which is movably extended from the mounting body between a releasing position and a securing position, having a head portion outwardly protruded from the second side of the mounting body; and 
     a locker unit provided at the mounting body for locking the coupling head in the releasing position and in the securing position, wherein in the releasing position, the head portion of the coupling head is locked in position for being disposed in an enlarged slot portion of the mounting slot, wherein after the locker unit is actuated to release the coupling head in the releasing position, the coupling head is moved to the securing position that the head portion of the coupling head is arranged for being slid to a narrower slot portion of the mounting slot for securing the accessory at the firearm. 
     In accordance with another aspect of the invention, the present invention comprises a KeyMod quick mounting arrangement, for detachably coupling an accessory at a firearm having a plurality of KeyMod mounting slots, comprising: 
     a mounting body having a first side adapted for extending from the accessory to be detachably coupled with the firearm, and an opposed second side; 
     a coupling head, which is movably extended from the mounting body between a releasing position and a securing position, having a head portion outwardly protruded from the second side of the mounting body, wherein in the releasing position, the head portion of the coupling head is arranged for being disposed in an enlarged slot portion of the mounting slot, and in the securing position, the head portion of the coupling head is arranged for being slid to a narrower slot portion of the mounting slot for securing the accessory at the firearm; and 
     a positioning member protruded from the second side of the mounting body at a position adjacent to the coupling head, wherein the positioning member is arranged for engaging with a second mounting slot adjacent to the mounting slot where the coupling head is engaged therewith. 
     Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
     These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a KeyMod quick mounting arrangement according to a preferred embodiment of the present invention. 
         FIG. 2  is a bottom view of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention, illustrating the coupling head in a releasing position. 
         FIG. 3  is a bottom view of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention, illustrating the coupling head in a securing position. 
         FIG. 4  is an exploded perspective view of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention. 
         FIG. 5  is a side sectional view of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention, illustrating the mounting operation of the arrangement to the KeyMod mounting slot and illustrating the accessory to be detachably mounted at the firearm via the arrangement. 
         FIG. 6  is a bottom sectional view of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention, illustrating the mounting operation of the arrangement to the KeyMod mounting slot. 
         FIG. 7  illustrates the first and second positioning members incorporating with the coupling head of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention. 
         FIGS. 7A to 7G  illustrates different configurations of the first and second positioning members incorporating with the coupling head of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention. 
         FIG. 8  illustrates a first alternative mode of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention. 
         FIG. 9  is a sectional view of the first alternative mode of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention. 
         FIG. 10  illustrates a second alternative mode of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention. 
         FIG. 11  is a sectional view of the second alternative mode of the KeyMod quick mounting arrangement according to the above preferred embodiment of the present invention. 
         FIG. 12  is an exploded perspective view of a KeyMod quick mounting arrangement according to a second preferred embodiment of the present invention. 
         FIG. 13  is a sectional view of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the releasing position. 
         FIG. 14  is a sectional view of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the securing position. 
         FIG. 15  is a sectional view of the coupling head of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the tapered shape of the coupling head with the resilient element. 
         FIG. 16  is a top view of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the arrangement mounted to the mounting slots to provide a three-point support. 
         FIG. 17  illustrates a first alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention. 
         FIG. 18  is a sectional view of the first alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the releasing position. 
         FIG. 19  is a sectional view of the first alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the securing position. 
         FIG. 20  is a sectional view of a second alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the releasing position. 
         FIG. 21  is a sectional view of the second alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the securing position. 
         FIG. 22  illustrates a third alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention. 
         FIG. 23  is a sectional view of the third alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the releasing position. 
         FIG. 24  is a sectional view of the third alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the securing position. 
         FIG. 25  is a plain view of the third alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the location of the releasable switch when the coupling head is moved in the releasing position. 
         FIG. 26  is a plain view of the third alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the location of the releasable switch when the coupling head is moved in the securing position. 
         FIG. 27  illustrates a fourth alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention. 
         FIG. 28  is a sectional view of the fourth alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention. 
         FIG. 29  illustrates a fifth alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the location of the releasable switch when the coupling head is moved in the releasing position. 
         FIG. 30  is a sectional view of the fifth alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the releasing position. 
         FIG. 31  is a perspective view of the fifth alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the location of the releasable switch when the coupling head is moved in the securing position. 
         FIG. 32  is a sectional view of the fourth alternative mode of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention, illustrating the coupling head in the securing position. 
         FIG. 33  illustrates an alternative mode of the resilient element of the KeyMod quick mounting arrangement according to the second preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description is disclosed to enable any person skilled in the art to make and use the present invention. Preferred embodiments are provided in the following description only as examples and modifications will be apparent to those skilled in the art. The general principles defined in the following description would be applied to other embodiments, alternatives, modifications, equivalents, and applications without departing from the spirit and scope of the present invention. 
     Referring to  FIGS. 1 to 7 , a KeyMod quick mounting arrangement according to a preferred embodiment of the present invention is illustrated, wherein the arrangement of the present invention is arranged for detachably coupling an accessory at a firearm having one or more KeyMod mounting slots  10 . For example, a micro-dot module is provided on the arrangement to detachably couple at the firearm as shown in  FIG. 5 . 
     For example, the firearm with a handguard provides a series of KeyMod mounting slots  10  aligning with a barrel axis of the firearm, wherein each of the mounting slots  10  has a Keyhole configuration to define an enlarged slot portion  11  and a narrower slot portion  12 . The accessory, such as laser module, scope mount, flashlight module, navigation light module, camera module, vertical grip, rail panel, hand stop, barricade support, can be detachably coupled at the firearm via the arrangement of the present invention. 
     According to the preferred embodiment, the arrangement of the present invention comprises a mounting body  20  and a coupling head  30 . 
     The mounting body  20  has a first side  21  arranged for extending from the accessory to be detachably coupled with the firearm, and an opposed second side  22  for coupling with the firearm at the mounting slot  10  via the coupling head  30 . The mounting body  20  further has two sidewalls  23 , a front side  24 , and a rear side  25  to define an interior cavity therewithin, and forms a low profile configuration to minimize a distance between the first and second sides  21 ,  22  so as to minimize the distance between the accessory and the firearm. As shown in  FIG. 5 , the micro-dot module, as an example, is provided on the first side  21  of the mounting body  20 . 
     The coupling head  30  is movably extended from the mounting body  10  and is moved between a releasing position and a securing position. In particular, the coupling head  30  has a head portion  31  outwardly protruded from the second side  22  of the mounting body  22 , a retention portion  32  received in the interior cavity of the mounting body  22 , and a neck portion  33  extended between the head portion  31  and the retention portion  32 . The coupling head  30  further has a slanted engaging surface  311  formed at the head portion  31  to the mounting slot  10  with a chamfered configuration. 
     The coupling head  30  further comprises a head adjustor  34  for adjusting a distance between the head portion  31  and the retention portion  32 . The head adjustor  34  comprises a threaded body  341  rotatably coupled at the retention portion  32  and an enlarged adjuster head  342  coupled at the head portion  31 , such that when the head adjustor  34  is rotated, the threaded body  341  rotated at the retention portion  32  to selectively adjust the distance between the head portion  31  and the retention portion  32 . Therefore, a portion of the threaded body  341  serves the neck portion  32  of the coupling head  30 . 
     Accordingly, in the releasing position, the head portion  31  of the coupling head  30  is arranged for being disposed in the enlarged slot portion  11  of the mounting slot  10 , and in the securing position, the head portion  31  of the coupling head  30  is arranged for being slid to the narrower slot portion  12  of the mounting slot  10  for securing the accessory at the firearm. In other words, the head portion  31  of the coupling head  30  is slid from the enlarged slot portion  11  of the mounting slot  10  to the narrower slot portion  12  thereof in order to couple the mounting body  20  at the firearm, so as to support the accessory at the firearm. 
     According to the preferred embodiment, the mounting body  20  is stationary when the coupling head  30  is moved between the releasing position and the securing position. In other words, after the head portion  31  of the coupling head  30  is disposed at the enlarged slot portion  11  of the mounting slot  10 , only the coupling head  30  is moved to slide the head portion  31  of the coupling head  30  to the narrower slot portion  12  of the mounting slot  10 . Therefore, the mounting body  20  is stationary during the sliding movement of the coupling head  30 . 
     In order to enable the sliding movement of the coupling head  30  when the mounting body  20  is stationary, the mounting body  20  further has an elongated guiding slot  26  formed at the second side  22  of the mounting body  20 . The coupling head  30  is slidably engaged at the guiding slot  26  in a position that the neck portion  33  of the coupling head  30  is slid along the guiding slot  26 , such that the head portion  31  of the coupling head  30  is outwardly protruded from the second side  22  of the mounting body  20  through the guiding slot  26  and is guided to slide at the guiding slot  26  between the releasing position and the securing position. 
     The guiding slot  26  is a through slot longitudinally formed at the second side  22  of the mounting body  20  to communicate the interior cavity of the mounting body  20  with an exterior thereof. Therefore, the coupling head  30  can be longitudinally moved with respect to the mounting head  20  via the guiding slot  26 , which is aligned with and parallel to the barrel axis of the firearm. In particular, the guiding slot  26  has a predetermined length to define two ends, wherein when the coupling head  20  is slid at one end of the guiding slot  26 , the coupling head  20  is retained in the releasing position, and when the coupling head  20  is slid at another end of the guiding slot  26 , the coupling head  20  is retained in the securing position. In other words, the length of the guiding slot  20  is corresponding to a distance of the mounting slot  10  between the enlarged slot portion  11  and the narrower slot portion  12 . It is worth mentioning that a width of the guiding slot  26  is slightly larger than a size of the neck portion  33  of the coupling head  30  and is smaller than a size of each of the retention portion  32  and the head portion  31  of the coupling head  30 . A distance between the retention portion  32  and the head portion  31  of the coupling head  30  is larger than a depth of the guiding slot  26 , i.e. the thickness of the bottom wall of the mounting body  10 . 
     According to the preferred embodiment, the coupling head  30  not only longitudinally moves with respect to the mounting head  20  but also vertically moves with respect to the mounting head  20  to adjust a distance between the head portion  31  of the coupling head  30  and the second side  22  of the mounting body  20 , as shown in  FIGS. 5 and 6 . In particular, when the coupling head  30  is moved in the securing position, the head portion  31  of the coupling head  30  is lifted toward the second side  22  of the mounting body  20 , such that a surrounding wall of the mounting slot  10  around the narrower slot portion  12  thereof will be sandwiched between the head portion  31  of the coupling head  30  and the second side  22  of the mounting body  20  so as to lock up the accessory at the firearm. 
     In particular, the mounting body  20  further has an elongated sliding channel  27  inclinedly formed at the mounting body  20 , wherein the coupling head  30  is guided to slide at the sliding channel  27  to move the head portion  31  of the coupling head  30  toward the second side  22  of the mounting head  20  for gradually minimizing the distance between the head portion  31  of the coupling head  30  and the second side  22  of the mounting head  20  when the head portion  31  of the coupling head  30  is moved from the releasing position to the securing position. In other words, when the head portion  31  of the coupling head  30  is moved from the releasing position to the securing position, the head portion  31  of the coupling head  30  is concurrently moved toward the second side  22  of the mounting body  20 . 
     As shown in  FIG. 4 , the sliding channel  27  is a through slot longitudinally and inclinedly formed at one of the sidewalls  23  of the mounting body  20  between the first and second sides  21 ,  22  thereof. Preferably, the sliding channel  27  is extended at 4 degrees with respect to the horizontal level. The inclination angle can be larger than 4 degrees depending on the desired vertical displacement of the head portion  31  of the coupling head  30 . It is appreciated that the sliding channel  27  can be formed at one of the front or rear wall  24 ,  25  of the mounting body  20 . The length of the sliding channel  27  must be equal or longer than the length of the guiding slot  26  to ensure the coupling head  20  to be moved between the releasing position and the securing position. It is worth mentioning that the guiding slot  26  is arranged to guide the longitudinally sliding movement of the coupling head  30  between the releasing position and the securing position. The sliding channel  27  is arranged to guide the vertical movement of the coupling head  30  to adjust the distance between the head portion  31  of the coupling head  30  and the second side  22  of the mounting head  20 . 
     The arrangement of the present invention further comprises an actuating member  40  for manually moving the coupling head  20  between the releasing position and the securing position. The actuating member  40  is movably coupled at the mounting body  20  to drive the coupling head  20  to move. In particular, the actuating member  40  is extended from the coupling head  20  to engage with the sliding channel  27 , such that when the actuating member  40  is moved at the sliding channel  27 , the coupling head  20  is driven not only to longitudinally slide along the guiding slot  26  but also to vertically move via the sliding channel  27 . 
     As shown in  FIGS. 2 to 4 , the actuating member  40  is pivotally coupled at the mounting body  20  to define a pivot point  401  thereat. The actuating member  40  has a driving end  41  extended into the interior cavity of the mounting body  20  to couple at the coupling head  30  and an actuating end  42  extended out of the sidewall  23  of the mounting body  20  through the sliding channel  27 . The driving end  41  of the actuating member  40  is rotatably coupled at the retention portion  32  of the coupling head  30 . 
     The pivot point  401  of the actuating member  40  is defined between the driving end  41  and the actuating end  42 . Therefore, by actuating the actuating end  42  of the actuating member  40 , the driving end  41  of the actuating member  40  is pivotally moved to drive the coupling head  30  between the releasing position and the securing position. It is worth mentioning that the actuating member  40  has an elongated pivot slot  402  formed thereat, wherein a pivot axle affixed at the pivot point  401  is engaged with the pivot slot  402 , so as to enable the driving end  41  of the actuating member  40  to move the coupling head  30  in a linear direction along the guiding slot  26  the pivotal movement of the actuating member  40 . 
     It is worth mentioning that during the pivotal movement of the actuating member  40 , the coupling head  20  is guided to longitudinally slide along the guiding slot  26 . At the same time, the pivotal movement of the actuating member  40  is guided by the sliding channel  27  in order to vertically move the head portion  31  of the coupling head  30  toward the second side  22  of the mounting head  20  when the coupling head  20  is guided to longitudinally slide along the guiding slot  26  from the releasing position to the securing position. In other words, one single actuating action of the actuating member  40  will move the head portion  31  of the coupling head  30  being slid to the narrower slot portion  12  of the mounting slot  10  and being moved toward the second side  22  of the mounting head  20  at the same time for securing the accessory at the firearm. 
     As shown in  FIGS. 2 to 4 , the arrangement further comprises a locker unit  50  provided at the mounting body  20  for locking the coupling head  30  in the securing position. According to the preferred embodiment, the locker unit  50  is also arranged to lock up the coupling head  30  in the releasing position. 
     According to the preferred embodiment, the locker unit  50  comprises a locking latch  51 , and first and second locking edges  52 ,  53  defined at the actuating member  40 . When the locking latch  51  is engaged with the first locking edge  52 , the coupling head  30  is locked in the releasing position, as shown in  FIG. 2 . When the locking latch  51  is engaged with the second locking edge  52 , the coupling head  30  is locked in the securing position, as shown in  FIG. 3 . 
     In particular, when the actuating member  40  is pivotally moved to drive the coupling head  30  in the releasing position, the actuating member  40  is moved in a position that the locking latch  51  is engaged with the first locking edge  52 . Likewise, when the actuating member  40  is pivotally moved to drive the coupling head  30  in the securing position, the actuating member  40  is moved in a position that the locking latch  51  is engaged with the second locking edge  53 . As a result, the coupling head  30  will be locked and stationary in each of the releasing position and the securing position. It is worth mentioning that after the locking latch  51  of the locker unit  50  is actuated to release the coupling head  30  in the releasing position, the coupling head  30  is allowed to move to the securing position that the head portion  31  of the coupling head  30  is slid to the narrower slot portion  12  of the mounting slot  10  for securing the accessory at the firearm. 
     As shown in  FIG. 4 , the locker unit  50  further has an elongated locking slot  54  formed at the sidewall  23  of the mounting body  20  and is integrally extended from the sliding channel  27  end-to-end, wherein the locking latch  51  is slidably engaged at the locking slot  54 . Preferably, the locking slot  54  is a horizontal through slot to communicate with the sliding channel  27 . 
     When the locking latch  51  is slid along the locking slot  51  toward the sliding channel  27 , the locking latch  51  is engaged with either the first or second locking edges  52 ,  53  at the actuating member  40 . When the locking latch  51  is slid along the locking slot  51  away from the sliding channel  27 , the locking latch  51  is disengaged with either the first or second locking edges  52 ,  53  so as to enable the pivotal movement of the actuating member  40 . 
     The locker unit  50  further comprises a resilient element  55  supported within the interior cavity of the mounting body  20  for applying an urging force against the locking latch  51 . The resilient element  55 , according to the preferred embodiment, is a compression spring having two ends biased against the locking latch  51  and an inner wall of the interior cavity of the mounting body  20  to push the locking latch  51  toward the sliding channel  27  along the locking slot  51 , so as to ensure the locking latch  51  to be engaged with either the first or second locking edges  52 ,  53  at the actuating member  40 . Therefore, the user must intentionally slide the locking latch  51  along the locking slot  54  to move the locking latch  51  away from the sliding channel  27  by overcoming the spring force of the resilient element  55  in order to disengage the locking latch  51  with either the first or second locking edges  52 ,  53 . 
     As shown in  FIG. 7 , the arrangement further comprises a positioning unit  60  for ensuring the corrected alignment between the accessory and the firearm and for preventing any unwanted longitudinal and/or rotational movement of the accessory with respect to the firearm after the mounting body  20  is mounted to the firearm. 
     The positioning unit  60  comprises a first positioning member  61  protruded from the second side  22  of the mounting body  20  at a position adjacent to the coupling head  30 , wherein the positioning member  61  is arranged for engaging with a second mounting slot  10 ′ adjacent to the mounting slot  10  where the coupling head  30  is engaged therewith. 
     The positioning unit  60  further comprises a second positioning member  62  protruded from the second side  22  of the mounting body  20  at a position adjacent to the coupling head  30 , wherein the second positioning member  62  is arranged for engaging with an edge of a third mounting slot  10 ″ adjacent to the mounting slot  10  where the coupling head  30  is engaged therewith. 
     According to the preferred embodiment, the first and second positioning members  61 ,  62  are integrally protruded from the second side  22  of the mounting body  20  and are aligned at a centerline of the guiding slot  26 , wherein the coupling head  30  is positioned between the two positioning members  61 ,  62 . In particular, the first and second positioning members  61 ,  62  are arranged to engage with the second and third mounting slots  10 ′,  10 ″ respectively, wherein the mounting slot  10  for the coupling head  30  is located between the second and third mounting slots  10 ′,  10 ″. 
     Preferably, the first positioning member  61  is sized and shaped with a keyhole configuration to match with the size and shape of the second mounting slot  10 ′, as shown in  FIG. 7 . The second positioning member  62  has a curved engaging edge  621  adapted for engaging with the edge of the third mounting slot  10 ″ at the narrower slot portion  12 ″ thereof, as shown in  FIG. 7 . Alternatively, the first and second positioning members  61 ,  62  can be configured with different shapes corresponding to the shapes of the second and third mounting slots  10 ′,  10 ″, as shown in  FIGS. 7A to 7G . For example, the size and shape of the first positioning member  61  can be configured to match with the enlarged slot portion  11 ′ of the second mounting slot  10 ′, as shown in  FIGS. 7A, 7B, and 7E . The size and shape of the second positioning member  62  can be configured to match with the narrower slot portion  12 ″ of the third mounting slot  10 ″, as shown in  FIG. 7B . The size and shape of the second positioning member  62  can be configured to match with the diameter size of the narrower slot portion  12 ″ of the third mounting slot  10 ″, as shown in  FIG. 7C . Likewise, the sizes and shapes of the first and second positioning members  61 ,  62  are configured to have a keyhole configuration to match with the sizes and shapes of the second and third mounting slots  10 ′,  10 ″, as shown in  FIG. 7D . Or, the size and shape of the second positioning member  62  can be configured to match with the diameter size of the enlarged slot portion  11 ″ of the third mounting slot  10 ″, as shown in  FIG. 7E . 
     It is worth mentioning that only one positioning member  61  can be used to incorporate with the coupling head  30  while the second positioning member  62  could be optional. For example, the first positioning member  61  can be formed in keyhole configuration to incorporate with the coupling head  30 , as shown in  FIG. 7F , or the first positioning member  61  can be formed to match with the enlarged slot portion  11 ′ of the second mounting slot  10 ′ in order to incorporate with the coupling head  30 , as shown in  FIG. 7G . 
     Preferably, both the first and second positioning members  61 ,  62  are used to incorporate with the coupling head  30 , such that the arrangement of the present invention provides a three-point support to prevent any unwanted longitudinal and/or rotational (twisting) movement of the accessory with respect to the firearm after the mounting body  20  is mounted to the firearm. 
     It is worth mentioning that since the coupling head  30  is locked in the releasing position, the first and second positioning members  61 ,  62  are automatically aligned with the second and third mounting slots  10 ′,  10 ″ respectively. In other words, in the releasing position, the distance between the coupling head  30  and the first positioning member  61 , and the distance between the coupling head  30  and the second positioning member  62  will not be altered. As a result, once the head portion  31  of the coupling head  30  is aligned at the enlarged slot portion  11  of the mounting slot  10 , the first and second positioning members  61 ,  62  will align with the second and third mounting slots  10 ′,  10 ″ respectively. This is the reason why the coupling head  30  should be locked and stationary in the releasing position. 
       FIGS. 8 and 9  illustrate a first alternative mode of the arrangement, wherein the actuating member  40 A is slidably coupled at the mounting body  20  at the sliding channel  27 . Accordingly, the actuating member  40 A has a driving end  41 A extended into the interior cavity of the mounting body  20  to couple at the coupling head  30  and an actuating end  42 A extended out of the sidewall  23  of the mounting body  20  through the sliding channel  27 . The driving end  41 A of the actuating member  40 A is affixed at the coupling head  30 . Therefore, by actuating the actuating end  42 A of the actuating member  40 A to slide the actuating member  40 A along the sliding channel  27 , the driving end  41 A of the actuating member  40 A is correspondingly moved to drive the coupling head  30  between the releasing position and the securing position. In other words, the coupling head  30  is guided to move from the releasing position to the securing position in order to move the head portion  31  of the coupling head  30  toward the bottom side  22  of the mounting body  20  at the same time. It is worth mentioning that one single actuating action of the actuating member  40 A will move the head portion  31  of the coupling head  30  being slid to the narrower slot portion  12  of the mounting slot  10  and being moved toward the second side  22  of the mounting head  20  at the same time for securing the accessory at the firearm. 
     It is appreciated that the actuating member  40 A can be extended out of the interior cavity of the mounting body  20  through the front wall thereof, wherein the actuating member  40 A can be pulled to move the coupling head  30  from the releasing position to the securing position and can be pushed to move the coupling head back to the releasing position from the securing position. Likewise, the actuating member  40 A can be extended out of the interior cavity of the mounting body  20  through the rear wall thereof, wherein the actuating member  40 A can be pushed to move the coupling head  30  from the releasing position to the securing position and can be pulled to move the coupling head back to the releasing position from the securing position. It is worth mentioning that, for the configuration of the actuating member  40 A at the front or rear side of the mounting body  20 , the sliding channel  27  can be formed as a rail supported in the interior cavity of the mounting to guide the head portion  31  of the coupling head  30  moving toward the bottom side  22  of the mounting body  20  when the coupling head  30  is moving in the securing position. 
     Furthermore, the locker unit  50 A has first and second locking slots  51 A,  52 A transversely extended from two ends of the sliding channel  27  to form a U-shaped configuration. When the actuating member  40 A is slid from the sliding channel  27  to the first locking slot  51 A, the coupling head  30  is locked in the releasing position, and when the actuating member  40 A is slid from the sliding channel  27  to the second locking slot  52 A, the coupling head  30  is locked in the securing position. 
     The locker unit  50 A further comprises a resilient element  55 A supported within the interior cavity of the mounting body  20  for applying an urging force against the actuating member  40 A. The resilient element  55 A, according to the preferred embodiment, is a compression spring having two ends biased against the actuating member  40 A and an inner wall of the interior cavity of the mounting body  20  to push the actuating member  40 A toward the first locking slot  51 A, so as to ensure the actuating member  40 A to be engaged with the first locking slot  51 A. Therefore, the user must intentionally slide the actuating member  40 A along the sliding channel  27  from the first locking slot  51 A by overcoming the spring force of the resilient element  55 A in order to push the actuating member  40 A toward the second locking slot  52 A. 
       FIGS. 10 and 11  illustrates a second alternative of the arrangement, wherein the guiding slot  26 B is modified to have a circular hole configuration formed at the bottom side  22  of the mounting body  20 . The diameter of the guiding slot  26 B is slightly larger than a size of the neck portion  33  of the coupling head  30  and is smaller than a size of each of the retention portion  32  and the head portion  31  of the coupling head  30 . Therefore, the coupling head  30  can only moved vertically at the guiding slot  26 B but cannot move longitudinally with respect to the mounting head  20 . 
     Accordingly, when the head portion  31  of the coupling head  30  is moved between the releasing position and the securing position, the mounting body  20  is correspondingly moved at the same direction. In other words, the coupling head  30  is locked in the releasing position via the guiding slot  26 B to prevent the coupling head  30  being slid with respect to the mounting body  20 . 
     The locker unit  50 B is provided at the mounting body  20  for locking the coupling head  30  in the securing position. The locker unit  50 B comprises a locking arm  52 B pivotally coupled at the mounting body  20  and a locking latch  51 B extended from the locking arm  52 B to couple at the coupling head  30  in order to lock up the coupling head  30  in the securing position and to move the head portion  31  of the coupling  30  toward the bottom side  22  of the mounting body  20  at the same time. 
     As shown in  FIG. 10 , the locking arm  52 B has a pivot end pivotally coupled at the mounting body  20  and an opposed movable end, wherein the locking arm  50 B is pivotally movable at the sliding channel  27 . The locking latch  51 B generally has a U-shaped configuration integrally extended from the locking arm  52 B, wherein when the movable end of the locking arm  52 B is actuated, the locking latch  51 B is extended into the interior cavity of the mounting body  20  through the sliding channel  27  and is engaged with the neck portion  33  of the coupling head  30  so as to move the head portion  31  of the coupling  30  toward the bottom side  22  of the mounting body  20 . It is worth mentioning that the locking latch  51 B is coupled at the coupling head  30  only when the coupling head  30  is moved in the securing position. Preferably, a first slanted surface  331  is formed at the neck portion  33  of the coupling head  30  and a second slanted surface  511 B is formed at the locking latch  51 B, such that when the locking latch  51 B is engaged with the neck portion  33  of the coupling head  30 , the second slanted surface  511 B is engaged with the first slanted surface  331  to move the head portion  31  of the coupling  30  toward the bottom side  22  of the mounting body  20 . Accordingly, the sliding channel  27  in this alternative can be an inclined channel or a horizontal channel formed at the sidewall  23  of the mounting body  20 . 
     The present invention further provides a method of detachably mounting the accessory at the firearm via the arrangement of the present invention. For the configuration of the coupling head  30  capable of longitudinally moving with respect to the mounting body  20  via the guiding slot  26 , the method comprises the following steps. 
     (1) Dispose the head portion  31  of the coupling head  30  at the enlarged slot portion  11  of the mounting slot  10 . Accordingly, the coupling head  30  is locked and stationary at the releasing position by the locker unit  50 , such that the user is able to easily align the head portion  31  of the coupling head  30  with the enlarged slot portion  11  of the mounting slot  10 . At the same time, the first and second positioning members  61 ,  62  are automatically aligned with the second and third mounting slots  10 ′,  10 ″ respectively. 
     (2) Slidably move the head portion  31  of the coupling head  30  from the enlarged slot portion  11  of the mounting slot  10  to the narrower slot portion  12  thereof so as to move the coupling head  30  from the releasing position to the securing position. It is worth mentioning that the mounting body  20  is stationary when the coupling head  30  is moved from the releasing position to the securing position along the guiding slot  26 . 
     Accordingly, the coupling head  30  is moved by the actuating member  40 . Preferably, when the actuating member  40  is pivotally actuated, the head portion  31  of the coupling head  30  not only moves to the narrower slot portion  12  of the mounting slot  10  but also moves toward the bottom side  22  of the mounting body  20 . Therefore, the surrounding wall around the mounting slot  10  is clamped between the head portion  31  of the coupling head  30  and the bottom side  22  of the mounting body  20 . 
     Alternatively, the coupling head  30  is moved by the actuating member  40 A, wherein the actuating member  40 A is slid along the sliding channel  27  to move the coupling head  30  between the releasing position and the securing position. 
     (3) Lock up the coupling head  30  in the securing position via the locker unit  50 . As a result, the accessory at first side  21  of the mounting body  20  can be securely mounted to the firearm. 
     In order to detach the accessory from the firearm, the user is able to unlock the coupling head  30  at the securing position via the locker unit  50  and move the head portion  31  of the coupling head  30  back to the enlarged slot portion  11  of the mounting slot  10  from the narrower slot portion  12  thereof. Therefore, the mounting body  20  can be detached from the firearm once the head portion  31  of the coupling head  30  is disengaged from the enlarged slot portion  11  of the mounting slot  10 . 
     The locking/unlocking operation of the arrangement comprises the following steps. 
     (A) Unlock the coupling head  30  in the releasing position to enable the coupling head  30  to move from the releasing position to the securing position. Accordingly, the coupling head  30  is normally locked up in the releasing position. In particular, the locking latch  51  is engaged with the first locking edge  52  at the actuating member  40  to retain the coupling head  30  in a stationary manner. Therefore, the head portion  31  of the coupling head  30  can be easily disposed at the enlarged slot portion  11  of the mounting slot  10 . 
     The locking latch  51  is moved until the locking latch  51  is disengaged with the first locking edge  52  at the actuating member  40 . Once the engagement between the locking latch  51  and the first locking edge  52  is released, the coupling head  30  can be moved from the releasing position to the securing position via the actuating arm  40 . 
     Alternatively, the actuating member  40 A is engaged with the first locking slot  51 A to retain the coupling head  30  in a stationary manner and to lock up the coupling head  30  in the releasing position. The actuating member  40 A is moved from the first locking slot  51 A to the sliding channel  27  in order to unlock the coupling head  30  in the releasing position, such that the coupling head  30  can be moved from the releasing position to the securing position via the actuating arm  40 A. 
     (B) Slidably move the head portion  31  of the coupling head  30  from the enlarged slot portion  11  of the mounting slot  10  to the narrower slot portion  12  thereof so as to move the coupling head  30  from the releasing position to the securing position. 
     (C) Lock up the coupling head  30  in the securing position. Accordingly, the locking latch  51  is engaged with the second locking edge  53  at the actuating member  40  to lock up the coupling head  30  in the securing position. It is worth mentioning that via the spring force of the resilient element  55 , the locking latch  51  is pushed to automatically engage with the second locking edge  53 , so as to ensure the coupling head  30  to be locked in the securing position. 
     In order to unlock the coupling head  30  in the securing position, the locking latch  51  is moved until the locking latch  51  is disengaged with the second locking edge  53 . Therefore, the coupling head  30  can be moved back in the releasing position via the actuating member  40 . Likewise, the spring force of the resilient element  55  will push the locking latch  51  to automatically engage with the first locking edge  52 , so as to ensure the coupling head  30  to be locked in the releasing position. 
     Alternatively, when the actuating member  40 A is slid from the sliding channel  27  to the second locking slot  52 A, the coupling head  30  is locked in the securing position. In order to unlock the coupling head  30  in the securing position, the actuating member  40 A is moved from the second locking slot  52 A back to the sliding channel  27 , so as to enable the coupling head  30  to be moved back to the releasing position. 
     For the configuration of the coupling head  30  capable of only moving in a vertical direction with respect to the mounting body  20  via the guiding slot  26 B, the method comprises the following steps. 
     (1) Dispose the head portion  31  of the coupling head  30  at the enlarged slot portion  11  of the mounting slot  10 . 
     (2) Slidably move the head portion  31  of the coupling head  30  from the enlarged slot portion  11  of the mounting slot  10  to the narrower slot portion  12  thereof so as to move the coupling head  30  from the releasing position to the securing position. It is worth mentioning that the mounting body  20  is moved to drive the coupling head  30  moving from the releasing position to the securing position. 
     Accordingly, when the head portion  31  of the coupling head  30  is moved in the securing position, the first and second positioning members  61 ,  62  are automatically aligned with the second and third mounting slots  10 ′,  10 ″ respectively. 
     (3) Lock up the coupling head  30  in the securing position via the locker unit  50 . Accordingly, when the locking arm  5 B is actuated, the locking latch  51 B is driven to engage with the neck portion  33  of the coupling head  30  so as to lock up the coupling head  30  in the securing position and to move the head portion  31  of the coupling  30  toward the bottom side  22  of the mounting body  20  at the same time. 
     It is worth mentioning that the arrangement according to the preferred embodiment and their alternatives are interchangeable such that the user is able to detachably mount the accessory to the firearm. For example, the coupling head  30  can be moved by the actuating member  40  or the actuating member  40 A while the coupling head  30  is locked by the locking latch  51 B. The actuating member  40 ,  40 A can be incorporated with any wall of the mounting body  20  except the first and second sides  21 ,  22  thereof. 
     As shown in  FIG. 12 , a KeyMod quick mounting arrangement according to a second embodiment of the present invention is illustrated as an alternative mode of the first embodiment. The arrangement according to the second embodiment is arranged for detachably coupling an accessory at a firearm having one or more KeyMod mounting slots  10 . For example, a hand grip is provided on the arrangement, as shown in  FIG. 12 , to detachably couple at the firearm. 
     According to the second embodiment, the KeyMod quick mounting arrangement comprises a mounting body  20 C, a positioning unit  60 C, and a coupling head  30 C. 
     The mounting body  20 C has a first side  21 C adapted for extending from the accessory to be detachably coupled with the firearm, and an opposed second side  22 C for coupling with the firearm at the mounting slot  10  via the coupling head  30 C. As shown in  FIG. 2 , the hand grip H, having a hollow structure, is integrally extended from the first side  21 C of the mounting body  20 C, wherein the hand grip H can be detachably coupled to the bottom side of the firearm when the arrangement of the present invention is coupled to the mounting slot  10  at the bottom side of the firearm. 
     The mounting body  20 C further has a sidewall  23 C between the first and second sides  21 C,  22 C, and forms a low profile configuration to minimize a distance between the first and second sides  21 C,  22 C so as to minimize the distance between the accessory and the firearm. Accordingly, the side surface of the hand grip H can be integrally extended from the sidewall  23  of the mounting body  20 C. 
     The positioning unit  60 C comprises a positioning member  61 C protruded from the second side  22 C of the mounting body  20 C for detachably engaging with the narrow slot portion  12  of the mounting slot  10 . In particular, the positioning member  61 C is upwardly protruded from the second side  22 C of the mounting body  20 C, as the orientation shown in  FIGS. 13, 14 and 16 , for slidably engaging with the narrow slot portion  12  of the mounting slot  10  from the enlarged slot portion  11  thereof. In other words, the positioning member  61 C is initially disposed at the enlarged slot portion  11  and is then slid to the narrow slot portion  12  of the mounting slot  10  in order to engage the positioning member  61 C with the mounting slot  10 . 
     The positioning unit  60 C further comprises a second positioning member  62 C protruded from the second side  22 C of the mounting body  20 C at a position adjacent to the coupling head  30 C. The first and second positioning member  61 C,  62 C are identical and are sized and shaped with a keyhole configuration to match with the size and shape of the narrow slot portion  12  of the mounting slot  10 . In particular, the first and second positioning members  61 C,  62 C are upwardly protruded from the second side  22 C of the mounting body  20 C and are aligned at a centerline of the second side  22 C of the mounting body  20 C, wherein the coupling head  30 C is positioned between the two positioning members  61 C,  62 C. Preferably, the first and second positioning members  61 C,  62 C are engaged with different mounting slots  10 . For example, the first and second positioning members  61 C,  62 C are engaged with the first and third mounting slots  10  respectively as shown in  FIG. 16 . 
     Each of the first and second positioning members  61 C,  62 C has an enlarged head portion and an elongated neck portion upwardly extended from the second side  22 C of the mounting body  20 C to the enlarged head portion. A size of the enlarged head portion of each of the first and second positioning members  61 C,  62 C is slightly larger than a width of the narrow slot portion  12  of the mounting slot  10 , and a size of the elongated neck portion of each of the first and second positioning members  61 C,  62 C is slightly smaller than the width of the narrow slot portion  12  of the mounting slot  10 . 
     Therefore, each of the first and second positioning members  61 C,  62 C can be slid to a far edge of the narrow slot portion  12  of the mounting slot  10  from the enlarged slot portion  11  thereof in order to engage with the narrow slot portion  12 . In particular, the enlarged head portion of each of the first and second positioning members  61 C,  62 C is arranged for sliding above the narrow slot portion  12  of the mounting slot  10  to engage the enlarged head portion of each of the first and second positioning members  61 C,  62 C with the slanted surface of the mounting slot  10  so as to secure the mounting body  20 C on the bottom side of the mounting slot  10 . Accordingly, each of the first and second positioning members  61 C,  62 C further has a slanted engaging surface formed at the enlarged head portion to slidably engage with the narrow slot portion  12  of the mounting slot  10  with the chamfered configuration. 
     According to the second embodiment, the coupling head  30 C is movably extended from the mounting body  20 C between a releasing position and a securing position. The coupling head  30 C has a head portion  31 C outwardly protruded from the second side  22 C of the mounting body  20 C. In the securing position, the head portion  31 C of the coupling head  30 C is arranged for being disposed in the enlarged slot portion  11  of the mounting slot  10  so as to secure the accessory at the firearm. In the releasing position, the head portion  31 C of the coupling head  30 C is arranged for disengaging with the enlarged slot portion  11  of the mounting slot  10  so as to enable the accessory to be detached from the firearm. 
     In particular, the coupling head  30 C is slidably coupled at the mounting body  20 C preferably in a vertically movable manner. Therefore, in the securing position, the head portion  31 C of the coupling head  30 C is slidably protruded from the second side  22 C of the mounting body  20 C for being disposed in the enlarged slot portion  11  of the mounting slot  10 . In other words, the top side of the head portion  31 C of the coupling head  30 C is protruded above the second side  22 C of the mounting slot  10  in the securing position. In the releasing position, the head portion  31 C of the coupling head  30 C is slid back to align with the second side  22 C of the mounting body  20 C for disengaging with the enlarged slot portion  11  of the mounting slot  10 . In other words, the top side of the head portion  31 C of the coupling head  30 C is located at the same level or below the second side  22 C of the mounting slot  10  in the releasing position. 
     As shown in  FIGS. 13, 14 and 16 , the coupling head  30 C is located between and is aligned with the first and second positioning members  61 C,  62 C. Preferably, after the first and second positioning members  61 C,  62 C are slidably engaged with the narrow slot portions  12  of the first and second mounting slots  10  respectively, the head portion  31 C of the coupling head  30 C is slidably protruded to engage with the enlarged slot portion  11  of the second mounting slot  10 . The second mounting slot  10  is located between and is aligned with the first and third mounting slots  10  end-to-end. Therefore, the arrangement of the present invention provides a three-point support to prevent any unwanted longitudinal and/or rotational (twisting) movement of the accessory with respect to the firearm after the mounting body  20 C is mounted to the firearm, as shown in  FIG. 16 . 
     In order to guide the sliding movement of the coupling head  30 C, the mounting body  20 C further has a sliding slot  26 C indently formed on the second side  22 C of the mounting body  20 C, wherein the coupling head  30 C is slidably disposed at the sliding slot  26 C to guide the coupling head  30 C to slide between the securing position and the releasing position. Preferably, the sliding slot  26 C is a through slot extended from the second side  22 C of the mounting body  20 C to the first side  21 C thereof. 
     As shown in  FIG. 15 , the head portion  31 C of the coupling head  30 C has a tapered circumferential surface that a circumferential size of the head portion  31 C is gradually reducing from bottom to top. Therefore, in the securing position, the tapered circumferential surface of the head portion  31 C of the coupling head  30 C is arranged for biasing against a rim of the enlarged slot portion  11  of the mounting slot  10 . It is worth mentioning that the tapered shaped head portion  31 C of the coupling head  30 C will match with the size of the enlarged slot portion  11  of the mounting slot  10  when the head portion  31 C of the coupling head  30 C is slidably protruded to engage with the enlarged slot portion  11  of the second mounting slot  10 , so as to prevent any unwanted movement between the mounting body  20 C and the firearm. 
     The KeyMod quick mounting arrangement further comprises a resilient element  70 C supported in the sliding slot  26 C for biasing against the coupling head  30 C to normally push the coupling head  30 C from the securing position to the releasing position, so as to ensure the coupling head  30 C to be normally retained at the releasing position. As shown in  FIG. 15 , the resilient element  70 C is a compression spring coaxially disposed in the sliding slot  26 C, wherein the resilient element  70 C has an upper end biased against an inner wall ridge of the sliding slot  26 C and a bottom end biased against an outer wall ridge of the coupling head  30 C. Therefore, the resilient element  70 C will apply a downward pushing force against the coupling head  30 C to push the coupling head  30 C down from the securing position to the releasing position. In other words, the coupling head  30 C will be normally retained in the releasing position via the resilient element  70 C. 
     According to the second embodiment, the KeyMod quick mounting arrangement further comprises an actuating unit  40 C for moving the coupling head  30 C between the securing position and the releasing position. The actuating unit  40 C comprises an actuating member  41 C pivotally coupled at the sidewall  23 C of the mounting body  20 C. The actuating member  41 C is actuated to push the head portion  31 C of the coupling head  30 C to be protruded from the second side  22 C of the mounting body  20 C in the securing position. The actuating member  41 C is also actuated to pull the head portion  31 C of the coupling head  30 C back to the second side  22 C of the mounting body  20 C in the releasing position. 
     As shown in  FIGS. 12 to 14 , the mounting body  20 C further has an actuating slot  27 C formed at the sidewall  23 C of the mounting body  20 C, wherein the actuating member  41 C is pivotally coupled at the sidewall  23 C of the mounting body  20 C within the actuating slot  27 C. 
     The actuating member  41 C is pivotally coupled at the mounting body  20 C to define a pivot point  401 C thereat. The actuating member  41 C has a pivot end pivotally coupled at the mounting body  20 C at the pivot point  401 C and a folding end to drive the actuating member  41 C in a pivotal movement at the pivot point  401 C. Accordingly, when the folding end of the actuating member  41 C is folded toward the sidewall  23 C of the mounting body  20 C, the coupling head  30 C is moved in the securing position. When the folding end of the actuating member  41 C is folded away from the sidewall  23 C of the mounting body  20 C, the coupling head  30 C is moved in the releasing position. 
     The actuating unit  40 C further comprises a transmission arm  42 C for transmitting the pivotal movement of the actuating member  41 C to a linear movement of the coupling head  30 C. Accordingly, the transmission arm  42 C has two ends pivotally coupled at the coupling head  31 C and the actuating member  41 C respectively. The first end (upper end) of the transmission arm  42 C is pivotally coupled at a bottom portion of the coupling head  31 C. The second end (lower end) of the transmission arm  42 C is pivotally coupled at the actuating member  41 C to define a second pivot point  402 C. Preferably, the first pivot point  401 C is located above the second pivot point  402 C. 
     Accordingly, when the actuating member  41 C is pivotally moved toward the sidewall  23 C of the mounting body  20 C, the transmission arm  42 C is pivotally actuated to push the head portion  31 C of the coupling head  30 C in the securing position, and when the actuating member  41 C is pivotally moved away from the sidewall  23 C of the mounting body  20 C, the transmission arm  42 C is pivotally actuated to pull the head portion  31 C of the coupling head  30 C in the releasing position. 
     In other words, when the folding end of the actuating member  41 C is folded toward the sidewall  23 C of the mounting body  20 C, the transmission arm  42 C is driven to move upwardly so as to push the coupling head  30 C upwardly in the securing position. Preferably, the actuating member  41 C is folded flat on the sidewall  23 C of the mounting body  20 C and is received within the actuating slot  27 C when the coupling head  30 C is moved in the securing position. 
     When the folding end of the actuating member  41 C is folded away from the sidewall  23 C of the mounting body  20 C, the transmission arm  42 C is driven to move downwardly so as to pull the coupling head  30 C downwardly in the releasing position. In other words, the coupling head  30 C is driven to reciprocatingly move within the sliding slot  26 C in a piston movement. 
     It is worth mentioning that when the user grips the hand grip as the accessory of the firearm, the hand of the user will tightly push the folding end of the actuating member  41 C toward the sidewall  23 C of the mounting body  20 C, so as to ensure the coupling head  30 C to be moved in the securing position when the hand grip is held by the user&#39;s hand. 
     The KeyMod quick mounting arrangement further comprises a locker unit  50 C for releasably locking the coupling head  30 C in the securing position. According to the second embodiment, the locker unit  50 C is arranged to lock up the actuating member  41 C at the sidewall  23 C of the mounting body  20 C in order to lock up the coupling head  30 C in the securing position. 
     Accordingly, the locker unit  50 C comprises a releasable switch  51 C movably coupled at the actuating member  41 C and a locking latch  52 C actuated by the releasable switch  51 C to releasably engage with the sidewall  23 C of the mounting body  20 C. As shown in  FIGS. 13 and 14 , the locking unit  50 C further has a locker slot  53 C formed at the actuating member  41 C and extended to the folding end of the actuating member  41 C, wherein the releasable switch  51 C is slidably disposed at the locker slot  53 C. The locking latch  52 C is extended from the releasable switch  51 C to an inner side of the sidewall  23 C of the mounting body  20 C. 
     When the folding end of the actuating member  41 C is folded toward the sidewall  23 C of the mounting body  20 C, the locking latch  52 C is moved to engage with an inner surface of the sidewall  23 C of the mounting body  20 C to lock up the actuating member  41 C at the sidewall  23 C of the mounting body  20 C, so as to lock up the coupling head  30 C in the securing position. 
     When the releasable switch  51 C is slidably and upwardly moved at the locker slot  53 C, i.e. the releasable switch  51 C is moved toward the pivot end of the actuating member  41 C from the folding end thereof, the locking latch  52 C is driven to disengage with the inner surface of the sidewall  23 C of the mounting body  20 C. Therefore, the folding end of the actuating member  41 C is allowed to pivotally move away from the sidewall  23 C of the mounting body  20 C so as to move the coupling head  30 C from the securing position to the releasing position. 
     Preferably, the locker unit  50 C further comprises a locker spring  54 C disposed in the locker slot  53 C for applying a pushing force against the releasable switch  51 C to push the releasable switch  51 C toward the folding end of the actuating member  41 C so as to ensure the locking latch  52 C to be engaged with the inner surface of the sidewall  23 C of the mounting body  20 C once the folding end of the actuating member  41 C is folded toward the sidewall  23 C of the mounting body  20 C. In other words, in order to unlock the locking latch  52 C, the releasable switch  51 C must be moved to against the force generated by the locker spring  54 C. It is worth mentioning that the bottom edge of the actuating slot  27 C has a curved surface to enable the locking latch  52 C to slide thereon in order to engage with the inner surface of the sidewall  23 C of the mounting body  20 C. 
       FIGS. 17 to 19  illustrate a first alternative mode of the actuating unit  40 D, wherein the actuating unit  40 D comprises an actuating member  41 D pivotally coupled at the sidewall  23 C of the mounting body  20 C at the actuating slot  27 C thereof. The actuating member  41 D has a pivot end pivotally coupled at the mounting body  20 C at the pivot point  401 D and a folding end to drive the actuating member  41 D in a pivotal movement at the pivot point  401 D. 
     The actuating member  41 D has trapezoid shaped and defines a top flat supporting surface  411 D and a pushing corner  412 D extended from the supporting surface  411 D. Accordingly, the distance between the supporting surface  411 D and the pivot point  401 D is shorter than the distance between the pushing corner  412 D and the pivot point  401 D. 
     When the folding end of the actuating member  41 D is pivotally moved toward the sidewall  23 C of the mounting body  20 C, the coupling head  30 C is pushed by the pushing corner  412 D of the actuating member  41 D in the securing position. It is worth mentioning that the bottom side of the coupling head  30 C is pushed by the pusher corner  412 D of the actuating member  41 D. When the folding end of the actuating member  41 D is pivotally moved away from the sidewall  23 C of the mounting body  20 C, the bottom side of the coupling head  30 C is supported by the supporting surface  411 D of the actuating member  41 D in the releasing position. Preferably, the pushing corner  412 D of the actuating member  41 D is a round corner, such that when the folding end of the actuating member  41 D is pivotally moved toward the sidewall  23 C of the mounting body  20 C, the pushing corner  412 D of the actuating member  41 D is pivotally slid at the bottom side of the coupling head  30 C in order to drive the coupling head  30 C between the securing position and the releasing position. 
     The locker unit  50 D is also provided for releasably locking the coupling head  30 C in the securing position, wherein the locker unit  50 D is arranged to lock up the actuating member  41 D at the sidewall  23 C of the mounting body  20 C in order to lock up the coupling head  30 C in the securing position. 
     The locker unit  50 D has a locking groove  501 D formed at the sidewall of the mounting body  20 C. In particular, the locking groove  501 D is indently formed at the bottom edge of the actuating slot  27 C. 
     The locker unit  50 D further comprises a releasable switch  51 D and a locking latch  52 D movably coupled at the actuating member  41 D, wherein the locking latch  52 D is actuated by the releasable switch  51 D to releasably engage with the locking groove  501 D at the sidewall  23 C of the mounting body  20 C. As shown in  FIGS. 18 and 19 , the locking unit  50 D further has a locker slot  53 D formed at the actuating member  41 D and extended to the folding end of the actuating member  41 D, wherein the locking latch  52 D is slidably disposed at the locker slot  53 C. The releasable switch  51 D is coupled to the locking latch  52 D and is slidably coupled at the outer surface of the actuating member  41 D. 
     When the folding end of the actuating member  41 D is pivotally moved to the sidewall  23 C of the mounting body  20 C, the locking latch  52 D is moved to engage with the locking groove  53 D to lock up the actuating member  41 D at the sidewall  23 C of the mounting body  20 C, so as to lock up the coupling head  30 C in the securing position. Accordingly, the locking latch  52 D is moved downwardly to engage with the locking groove  53 D. 
     When the releasable switch  51 D is moved upwardly, the locking latch  52 D is driven to move upwardly for disengaging with the locking groove  53 D. When the locking latch  52 D is moved to disengage with the locking groove  53 D, the folding end of the actuating member  41 D is allowed to be pivotally moved away from the sidewall  23 C of the mounting body  20 C so as to move the coupling head  30 C from the securing position to the releasing position. 
     Preferably, the locker unit  50 D further comprises a locker spring  54 D disposed in the locker slot  53 D for applying a pushing force against the locking latch  52 D to push the locking latch  52 D toward the locking groove  53 D so as to ensure the locking latch  52 D to be engaged with the locking groove  53 D once the folding end of the actuating member  41 D is folded toward the sidewall  23 C of the mounting body  20 C. In other words, in order to unlock the locking latch  52 D, the releasable switch  51 D must be moved to against the force generated by the locker spring  54 D. It is worth mentioning that the bottom edge of the actuating slot  27 C has a slanted surface to enable the locking latch  52 D to slide thereon in order to engage with the locking groove  53 D. 
       FIGS. 20 and 21  illustrate a second alternative mode of the actuating unit  40 E, wherein the actuating unit  40 E comprises an actuating member  41 E pivotally coupled at the sidewall  23 C of the mounting body  20 C at the actuating slot  27 C thereof. The actuating member  41 E has a pivot end pivotally coupled at the mounting body  20 C at the pivot point  401 E and a folding end to drive the actuating member  41 E in a pivotal movement at the pivot point  401 E. 
     The actuating member  41 E has a top flat supporting surface  411 E and a side flat supporting surface  412 E. Accordingly, the distance between the top flat supporting surface  411 E and the pivot point  401 E is larger than the distance between the side flat supporting surface  412 E and the pivot point  401 E. 
     When the folding end of the actuating member  41 E is pivotally moved toward the sidewall  23 C of the mounting body  20 C, the coupling head  30 C is pushed by the top flat supporting surface  411 E of the actuating member  41 E in the securing position. It is worth mentioning that the bottom side of the coupling head  30 C is pushed by the top flat supporting surface  411 E of the actuating member  41 E. When the folding end of the actuating member  41 E is pivotally moved away from the sidewall  23 C of the mounting body  20 C, the bottom side of the coupling head  30 C is supported by the side flat supporting surface  412 E of the actuating member  41 E in the releasing position. 
     The actuating member  41 E further has a guiding corner  413 E extended between the top flat supporting surface  411 E and the side flat supporting surface  412 E. 
     Preferably, the guiding corner  413 E of the actuating member  41 E is a round corner, such that when the folding end of the actuating member  41 E is pivotally moved toward or away from the sidewall  23 C of the mounting body  20 C, the bottom side of the coupling head  30 C is guided to slide between the top flat supporting surface  411 E and the side flat supporting surface  412 E through the guiding corner  413 E in order to drive the coupling head  30 C between the securing position and the releasing position. 
     The locker unit  50 E is also provided for releasably locking the coupling head  30 C in the securing position, wherein the locker unit  50 E is arranged to lock up the actuating member  41 E at the sidewall  23 C of the mounting body  20 C in order to lock up the coupling head  30 C in the securing position. 
     The locker unit  50 E has a locking groove  501 E formed at the sidewall of the mounting body  20 C. In particular, the locking groove  501 E is indently formed at the bottom edge of the actuating slot  27 C. 
     The locker unit  50 E further comprises a releasable switch  51 E and a locking latch  52 E movably coupled at the actuating member  41 E, wherein the locking latch  52 E is actuated by the releasable switch  51 E to releasably engage with the locking groove  501 E at the sidewall  23 C of the mounting body  20 C. As shown in  FIGS. 20 and 21 , the locking unit  50 E further has a locker slot  53 E formed at the actuating member  41 E and extended to the folding end of the actuating member  41 E, wherein the locking latch  52 E is slidably disposed at the locker slot  53 E. The releasable switch  51 E is coupled to the locking latch  52 E and is slidably coupled at the outer surface of the actuating member  41 E. 
     When the folding end of the actuating member  41 E is pivotally moved to the sidewall  23 C of the mounting body  20 C, the locking latch  52 E is moved to engage with the locking groove  53 E to lock up the actuating member  41 E at the sidewall  23 C of the mounting body  20 C, so as to lock up the coupling head  30 C in the securing position. Accordingly, the locking latch  52 E is moved downwardly to engage with the locking groove  53 E. 
     When the releasable switch  51 E is moved upwardly, the locking latch  52 E is driven to move upwardly for disengaging with the locking groove  53 E. When the locking latch  52 E is moved to disengage with the locking groove  53 E, the folding end of the actuating member  41 E is allowed to be pivotally moved away from the sidewall  23 C of the mounting body  20 C so as to move the coupling head  30 C from the securing position to the releasing position. 
     Preferably, the locker unit  50 E further comprises a locker spring  54 E disposed in the locker slot  53 E for applying a pushing force against the locking latch  52 E to push the locking latch  52 E toward the locking groove  53 E so as to ensure the locking latch  52 E to be engaged with the locking groove  53 E once the folding end of the actuating member  41 E is folded toward the sidewall  23 C of the mounting body  20 C. In other words, in order to unlock the locking latch  52 E, the releasable switch  51 E must be moved to against the force generated by the locker spring  54 E. It is worth mentioning that the bottom edge of the actuating slot  27 C has a slanted surface to enable the locking latch  52 E to slide thereon in order to engage with the locking groove  53 E. 
       FIGS. 22 to 26  illustrate a third alternative mode of the actuating unit  40 F, wherein the actuating unit  40 F comprises an actuating member  41 F pivotally coupled at the sidewall  23 C of the mounting body  20 C at the actuating slot  27 C thereof. The actuating member  41 F has a pivot end pivotally coupled at the mounting body  20 C at the pivot point  401 F and a folding end to drive the actuating member  41 F in a pivotal movement at the pivot point  401 F. 
     The actuating member  41 F has a top flat supporting surface  411 F and a side flat supporting surface  412 F. Accordingly, the distance between the top flat supporting surface  411 F and the pivot point  401 F is larger than the distance between the side flat supporting surface  412 F and the pivot point  401 F. 
     When the folding end of the actuating member  41 F is pivotally moved toward the sidewall  23 C of the mounting body  20 C, the coupling head  30 C is pushed by the top flat supporting surface  411 F of the actuating member  41 F in the securing position. It is worth mentioning that the bottom side of the coupling head  30 C is pushed by the top flat supporting surface  411 F of the actuating member  41 F. When the folding end of the actuating member  41 F is pivotally moved away from the sidewall  23 C of the mounting body  20 C, the bottom side of the coupling head  30 C is supported by the side flat supporting surface  412 F of the actuating member  41 F in the releasing position. 
     The actuating member  41 F further has a guiding corner  413 F extended between the top flat supporting surface  411 F and the side flat supporting surface  412 F. 
     Preferably, the guiding corner  413 F of the actuating member  41 F is a round corner, such that when the folding end of the actuating member  41 F is pivotally moved toward or away from the sidewall  23 C of the mounting body  20 C, the bottom side of the coupling head  30 C is guided to slide between the top flat supporting surface  411 F and the side flat supporting surface  412 F through the guiding corner  413 F in order to drive the coupling head  30 C between the securing position and the releasing position. 
     The locker unit  50 F is also provided for releasably locking the coupling head  30 C in the securing position, wherein the locker unit  50 F is arranged to lock up the actuating member  41 F at the sidewall  23 C of the mounting body  20 C in order to lock up the coupling head  30 C in the securing position. 
     The locking unit  50 F has a locking indention  501 F formed at the actuating member  41 F and comprises a resilient arm  52 F supported within the mounting body  20 C at a position that a free end of the resilient arm  52 F is engaged with the locking indention  501 F to lock up the coupling head  30 C in the securing position when the actuating member  41 F is pivotally moved to the sidewall  23 C of the mounting body  20 C. 
     The locking indention  501 F is formed at the inner corner portion of the actuating member  41 F which is extended from the top flat supporting surface  411 F thereof. The resilient arm  52 F is a flexible flat metal panel having an affixing end affixed to the mounting body  20 C, wherein the free end of the resilient arm  52 F is extended toward the sidewall  23 C of the mounting body  20 C. Accordingly, the free end of the resilient arm  52 F is normally engaged with the locking indention  501 F to lock up the pivotally movement of the actuating member  41 F. Once the free end of the resilient arm  52 F is bent upwardly, the free end of the resilient arm  52 F is disengaged with the locking indention  501 F, so as to allow the pivotally movement of the actuating member  41 F. 
     The locking unit  50 F further comprises a releasable switch  51 F slidably coupled at the mounting body  20 C to bend the free end of the resilient arm  52 F for disengaging with the locking indention  501 F so as to enable the actuating member  41 F to be pivotally moved away from the sidewall  23 C of the mounting body  20 C in order to move the coupling head  30 C from the securing position to the releasing position. 
     As shown in  FIGS. 24 to 26 , the releasable switch  51 F is an elongated member transversely extended from the mounting body  20 C in a slidably movable manner. The releasable switch  51 F has a slender portion  511 F and a thicken portion  512 F integrally extended from the slender portion  511 F, wherein a size of the thicken portion  512 F larger than a size of the slender portion  511 F. Accordingly, when the free end of the resilient arm  52 F is rested on the slender portion  511 F of the releasable switch  51 F, as shown in  FIG. 26 , the resilient arm  52 F forms a straight and non-bent member that the free end of the resilient arm  52 F is engaged with the locking indention  501 F. When the releasable switch  51 F is actuated to slide transversely, the free end of the resilient arm  52 F shifted from the slender portion  511 F of the releasable switch  51 F to rest on the thicken portion  512 F thereof. As a result, the free end of the resilient arm  52 F is bent upwardly by the thicken portion  512 F of the releasable switch  51 F to disengage with the locking indention  501 F. Preferably, the releasable switch  51 F has two thicken portions  512 F, wherein the slender portion  511 F is integrally extended between the two thicken portions  512 F, such that the releasable switch  51 F can be transversely moved at either direction to shift the free end of the resilient arm  52 F from the slender portion  511 F of the releasable switch  51 F to one of the thicken portions  512 F thereof. 
     It is worth mentioning that when the releasable switch  51 F is actuated to slide transversely to bend the free end of the resilient arm  52 F, the actuating member  41 F is also pushed downwardly at the locking indention  501 F by the releasable switch  51 F so as to pivotally move the actuating member  41 F away from the sidewall  23 C of the mounting body  20 C at the same time. It is appreciated that a coil spring can be coupled at the pivot point  401 F to pivotally move the actuating member  41 F away from the sidewall  23 C of the mounting body  20 C. 
       FIGS. 27 and 28  illustrate a fourth alternative mode of the actuating unit  40 G for moving the coupling head  30 C between the securing position and the releasing position. The actuating unit  40 G comprises an actuating member  41 G which is extended from the coupling head  30 C and is rotatably coupled with the mounting body  20 C. 
     In particular, the actuating member  41 G is integrally and downwardly extended from the coupling head  30 C, wherein an outer threaded portion  42 G is formed at the actuating member  41 G to rotatably engage with an inner thread portion  43 G formed at an inner wall of the sliding slot  26 C of the mounting body  20 C. When the actuating member  41 G is rotated at one direction, the head portion  31 C of the coupling head  30 C is moved to be protruded from the second side  22 C of the mounting body  20 C in the securing position. When the actuating member  41 G is rotated at an opposite direction, the head portion  31 C of the coupling head  30 C is moved back to the second side  22 C of the mounting body  20 C in the releasing position. Preferably, an actuating slot  411 G is formed at the bottom side of the actuating member  41 G in order to drive the actuating member  41 G. 
       FIGS. 29 and 32  illustrate a mounting ring arrangement serving as the accessory to be mounted at the firearm via the arrangement of the present invention as another example.  FIGS. 29 and 32  also illustrate a fifth alternative mode of the actuating unit  40 H for moving the coupling head  30 C between the securing position and the releasing position. The actuating unit  40 H comprises an actuating member  41 H transversely and rotatably supported at the mounting body  20 C at a position that a rotatable axle  401 H is located off-center of the actuating member  41 H. In particular, the actuating member  41 H has a driving portion  411 H defined at the longest distance between an circumferential surface and the rotatable axle  401 H and a releasing portion  412 H defined at the shortest distance between the circumferential surface and the rotatable axle  401 H. 
     The actuating unit  40 H further comprises a releasable switch  42 H coupled at the actuating member  41 H at the rotatable axle  401 H to drive the actuating member  41 H to rotate. When the releasable switch  42 H is rotated at one direction about the rotatable axle  401 H, as shown in  FIG. 31 , the head portion  31 C of the coupling head  30 C is moved to be protruded from the second side  22 C of the mounting body  20 C by the driving portion  411 H of the actuating member  41 H, as shown in  FIG. 32 . When the releasable switch  41 H is rotated at an opposite direction, as shown in  FIG. 29 , the head portion  31 C of the coupling head  30 C is moved back to the second side  22 C of the mounting body  20 C by the releasing position  412 H of the actuating member  41 H, as shown in  FIG. 30 . 
       FIG. 33  illustrates an alternative mode of the resilient element  70 J which is supported in the sliding slot  26 C for biasing against the coupling head  30 C to normally push the coupling head  30 C from the releasing position to the securing position, so as to ensure the coupling head  30 C to be normally retained at the securing position. 
     As shown in  FIG. 33 , the resilient element  70 J is a compression spring coaxially disposed in the sliding slot  26 C, wherein the resilient element  70 J has a bottom end biased against an inner wall ridge of the sliding slot  26 C and an upper end biased against an outer wall ridge of the coupling head  30 C. Therefore, the resilient element  70 J will apply an upward pushing force against the coupling head  30 C to push the coupling head  30 C up to the securing position from the releasing position. In other words, the coupling head  30 C will be normally retained in the securing position via the resilient element  70 J. 
     Therefore, the difference between the resilient element  70 C as shown in  FIGS. 12 to 32  and the resilient element  70 J as shown in  FIG. 33  is that the coupling head  30 C will be normally retained in the releasing position via the resilient element  70 C while the coupling head  30 C will be normally retained in the securing position via the resilient element  70 J. As a result, the user must actuate the actuating member to move the coupling head  30 C in the securing position by applying a force against the force of the resilient element  70 C. Alternatively, the user must actuate the actuating member to move the coupling head  30 C in the releasing position by applying a force against the force of the resilient element  70 J. It is worth mentioning that the resilient element  70 J can be used as a replacement of the resilient element  70 C as shown in  FIGS. 12 to 32 , such that the configurations between the resilient element  70 C and resilient element  70 J are interchangeable. 
     In view of the second embodiment and its alternatives, the accessory is stationary when the coupling head  30 C is moved between the securing position and the releasing position. Therefore, once the positioning members  61 C,  62 C are slid to engage with the mounting slots  10  respectively, the mounting body  20 C and the accessory will stationary to prevent any unwanted disengagement between the positioning members  61 C,  62 C and the mounting slots  10 . Then, the user is able to actuate the actuating member to move and lock the coupling head  30 C with the mounting slot  10 , so as to secure the accessory at the firearm. The user is able to quickly release the accessory from the firearm by simply disengaging the coupling head  30 C with the mounting slot  10  via the actuating unit and by slidably disengaging the positioning members  61 C,  62 C with the mounting slots  10 . 
     One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting. 
     It will thus be seen that the objects of the present invention have been fully and effectively accomplished. The embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.