Patent Publication Number: US-2022226977-A1

Title: Powered fastener driver

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to co-pending U.S. Provisional Patent Application No. 63/180,722 filed on Apr. 28, 2021, U.S. Provisional Patent Application No. 63/151,240 filed on Feb. 19, 2021, and U.S. Provisional Patent Application No. 63/139,549 filed on Jan. 20, 2021, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a powered fastener driver, and more particularly to a battery powered fastener driver. 
     BACKGROUND OF THE INVENTION 
     There are various fastener drivers known in the art for driving fasteners (e.g., nails, tacks, staples, etc.) into a workpiece. These fastener drivers operate utilizing various means known in the art (e.g., compressed air generated by an air compressor, electrical energy, a flywheel mechanism, etc.), but often these designs are met with power, size, and cost constraints. 
     SUMMARY OF THE INVENTION 
     The present invention provides, in one aspect, a fastener driver comprising a housing defining a head portion and a handle portion, a drive mechanism positioned within the housing, and a firing mechanism including a primary guide member supported within the head portion of the housing, a secondary guide member spaced from the primary guide member and supported within the head portion of the housing, a piston slidable along the primary guide member and the secondary guide member, a driver blade attached to the piston and configured to be movable along a drive axis. A biasing member configured to move the piston and the driver blade from a top dead center (TDC) position toward a bottom dead center (BDC) position and a lifter assembly operated by the drive mechanism to return the piston and the driver blade towards the TDC position, against the bias of the biasing member. 
     The invention provides, in another aspect, a fastener driver comprising a housing defining a head portion and a handle portion; a drive mechanism positioned within the housing; a firing mechanism including a primary guide member supported within the head portion of the housing, a piston slidable along the primary guide member, a driver blade attached to the piston, and a biasing member configured to move the piston and the driver blade from a top dead center (TDC) position toward a bottom dead center (BDC) position; a lifter assembly operated by the drive mechanism to return the piston and the driver blade towards the TDC position, against the bias of the biasing member; and a frame located within the housing and configured to support the lifter assembly and the primary guide member. 
     The invention provides, in another aspect, a fastener driver comprising a housing defining a head portion and a handle portion; a drive mechanism positioned within the housing; a firing mechanism including a piston and a driver blade that are moveable from a top dead center (TDC) position toward a bottom dead center (BDC) position; and a lifter assembly operated by the drive mechanism to rotate about a rotational axis to return the piston and the driver blade towards the TDC position, the lifter assembly including a first eccentric pin located at a first radial distance relative to the rotational axis, and a second eccentric pin located at a second radial distance relative to the rotational axis, the second radial distance being less than the first radial distance. 
     The invention provides, in another aspect, a fastener driver comprising a magazine configured to receive fasteners therein, the magazine including a magazine cover having a length extending along a longitudinal axis between a first end and a second end, a top surface having an opening defined therein proximate the second end, and a bottom surface opposite the top surface, and a magazine body slidably movable relative to the magazine cover from a closed position to an open position for reloading the magazine with fasteners; a nosepiece including a fastener driving channel from which consecutive fasteners from the magazine are driven, the nosepiece adjacent the first end of the magazine cover; a latch coupled to the top surface of the magazine cover, the latch extending through the opening in the top surface of the magazine cover, the latch including a latch projection that defines a first contact surface; a pusher body slidably coupled to the magazine body, the pusher body including an arm member that defines a second contact surface; and a biasing member configured to bias the pusher body and the fasteners within the magazine toward the nosepiece when the magazine body is in the closed position, wherein the first and second contact surfaces are engageable to hold the pusher body in a latched position when the magazine body is in the open position. 
     The invention provides, in another aspect, a fastener driver comprising a fastener driver comprising a magazine configured to receive collated fastener strips therein, the magazine including a magazine cover having a length extending along a longitudinal axis between a first end and a second end, a top surface, parallel side walls respectively extending from opposite sides of the top surface, and a rib extending inward from at least one of the side walls along a first portion of the length of the magazine cover, the magazine cover configured to receive the collated fastener strips between the side walls along a second portion of the length of the magazine cover, the rib configured to restrict installation or removal of the collated fastener strips located within the first portion of the length of the magazine cover, and a magazine body slidably movable relative to the magazine cover from a closed position to an open position for reloading the magazine with collated fastener strips; and a nosepiece including a fastener driving channel from which consecutive fasteners from the magazine are driven, the nosepiece adjacent the first end of the magazine cover. 
     The invention provides, in another aspect, a fastener driver comprising a magazine configured to receive collated fastener strips therein, the magazine including a magazine cover having a length extending along a longitudinal axis between a first end and a second end, a top surface, parallel side walls respectively extending from opposite sides of the top surface, and a rib extending inward from at least one of side walls along the length of the magazine cover, the magazine cover configured to receive the collated fastener strips through the second end of the magazine cover and between the side walls, the rib configured to restrict installation or removal of the collated fastener strips after being inserted through the second end of the magazine cover, and a magazine body slidably movable relative to the magazine cover from a closed position to an intermediate position, and pivotable relative to the magazine cover from the intermediate position to an open position for reloading the magazine; and a nosepiece including a fastener driving channel from which consecutive fasteners from the magazine are driven, the nosepiece adjacent the first end of the magazine cover. 
     The invention provides, in another aspect, a fastener driver comprising a housing defining a head portion and a handle portion; a drive mechanism positioned within the housing; a firing mechanism including a piston and a driver blade that are moveable from a top dead center (TDC) position toward a bottom dead center (BDC) position; and a lifter assembly operated by the drive mechanism to rotate about a rotational axis, the lifter assembly including a unitary body having an input shaft that is coupled to the drive mechanism to receive torque therefrom and a hub that selectively engages a portion of the firing mechanism to return the piston and the driver blade towards the TDC position. 
     The invention provides, in another aspect, a fastener driver comprising a magazine having a length extending along a longitudinal axis between a first end and a second end, the magazine configured to receive a collated fastener strip therein, the collated fastener strip including a plurality of fasteners having a crown section and a tip opposing the crown section; a nosepiece including a fastener driving channel from which consecutive fasteners from the magazine are driven, the nosepiece located adjacent the first end of the magazine; and a fastener alignment mechanism positioned adjacent the first end of the magazine, the fastener alignment mechanism including a magnetic element that produces a magnetic force on the tip of the fastener adjacent the fastener driving channel to urge the tip of the fastener towards the nosepiece, wherein the magnetic force urges the fastener towards a loading position in which the fastener aligns with the fastener driving channel of the nosepiece. 
     The invention provides, in another aspect, a fastener driver comprising a magazine having a length extending along a longitudinal axis between a first end and a second end, the magazine configured to receive a collated fastener strip therein; and a nosepiece including a fastener driving channel from which consecutive fasteners from the magazine are driven, the nosepiece located adjacent the first end of the magazine, the nosepiece including an interior surface configured to receive a cable being secured to a workpiece during a fastener driving operation, the interior surface including a first portion having a first width and a second portion having a second width, the second width being greater than the first width. 
     The invention provides, in another aspect, a fastener driver comprising a housing defining a head portion and a handle portion; an end cap supported within the head portion, the end cap including a first recess, a second recess surrounded by the first recess, and an outer sleeve surrounding the first recess; a drive mechanism positioned within the housing; a firing mechanism including a piston, a driver blade attached to the piston, a first biasing member having a first end supported within the piston and a second end seated within the first recess of the end cap, and a second biasing member having a first end supported within the piston and a second end seated within the second recess of the end cap, the first and second biasing members configured to move the piston and the driver blade from a top dead center (TDC) position toward a bottom dead center (BDC) position; a washer positioned between the second end of the first biasing member and the end cap, the washer being supported within the first recess of the end cap; and a lifter assembly operated by the drive mechanism to return the piston and the driver blade towards the TDC position, against the bias of the first and second biasing members. 
     The invention provides, in another aspect, a fastener driver comprising A fastener driver comprising a front end a housing defining a head portion having a rear end and a handle portion; a drive mechanism positioned within the housing; a battery pack coupled to a battery receptacle, the battery pack configured to provide power to the drive mechanism; and a firing mechanism including a piston, and a driver blade attached to the piston, the driver blade configured to move from a top dead center (TDC) position toward a bottom dead center (BDC) position, wherein the fastener driver has a length defined between the front end and the rear end, and wherein the length is less than or equal to 18 centimeters. 
     The invention provides, in another aspect a fastener driver comprising a housing defining a head portion and a handle portion; a drive mechanism positioned within the housing; a firing mechanism configured to be actuated in response to an input from the drive mechanism, the firing mechanism including a piston, a driver blade attached to the piston, and a biasing member configured to move the piston and the driver blade from a top dead center (TDC) position toward a bottom dead center (BDC) position, wherein the biasing member stores at least 14.5 Joules of energy when the driver blade is in the TDC position. 
     Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a powered fastener driver. 
         FIG. 2  is a side view of the powered fastener driver of  FIG. 1 , with portions removed for clarity, illustrating a drive mechanism, a firing mechanism, and a lifter assembly. 
         FIG. 3  is a side view of the drive mechanism, the firing mechanism, and the lifter assembly of the powered fastener driver of  FIG. 1 . 
         FIG. 4  is a perspective view of a portion of the lifter assembly and the firing mechanism of  FIG. 3 . 
         FIG. 5  is a perspective view of the portion of the lifter assembly shown in  FIG. 4 . 
         FIG. 6  is a top view of the portion of the lifter assembly shown in  FIG. 4 . 
         FIG. 7  is a perspective view of a magazine of the powered fastener driver of  FIG. 1 , illustrating the magazine in a closed position. 
         FIG. 8  is another perspective view of the magazine of  FIG. 7 , illustrating the magazine in an open position. 
         FIG. 9  is a cross-sectional view of the magazine of  FIG. 7  along section line  7 - 7  in  FIG. 7 . 
         FIG. 10  is another perspective view of the magazine of  FIG. 7 , illustrating a pusher latch. 
         FIG. 11  is another perspective view the magazine of  FIG. 7 , with a portion of the magazine removed for clarity to illustrate the pusher latch and a pusher body. 
         FIG. 12  is a side view of the pusher latch and pusher body. 
         FIG. 13  is a top perspective view of the pusher latch and pusher body of  FIG. 12 . 
         FIG. 14  is a top perspective view of another embodiment of a magazine for use with the powered fastener driver of  FIG. 1 , illustrating the magazine in a closed position. 
         FIG. 15  is a bottom perspective view of the magazine of  FIG. 14 , illustrating the magazine in an open position. 
         FIG. 16  is an enlarged, bottom perspective view of the magazine of  FIG. 15 . 
         FIG. 17  is a cross-sectional view of the magazine of FIG. through section  16 - 16  in  FIG. 14 . 
         FIG. 18  is a bottom perspective view of a powered fastener driver including another embodiment of a magazine in a closed position. 
         FIG. 19  is a bottom perspective view of the powered fastener driver of  FIG. 18  with the magazine in an open position. 
         FIG. 20  is a bottom perspective view of the magazine of  FIG. 18 , illustrating the magazine in a partially open, intermediate position. 
         FIG. 21  is a bottom perspective view of the magazine of  FIG. 18 , illustrating the magazine in a fully open position. 
         FIG. 22  is a cross-sectional view of the magazine of  FIG. 18  through section  22 - 22  in  FIG. 18 . 
         FIG. 23  is a cross-sectional view of a powered fastener driver according to another embodiment, illustrating a drive mechanism, a firing mechanism, and a lifter assembly. 
         FIG. 24  is a side view of the drive mechanism, the firing mechanism, and the lifter assembly of the powered fastener driver of  FIG. 23 . 
         FIG. 25  is a perspective view of the lifter assembly of the power fastener driver of  FIG. 23 . 
         FIG. 26  is a cross-sectional view of a portion of the power fastener driver of  FIG. 23 , illustrating a fastener alignment mechanism. 
         FIG. 27  is a front view of a portion of the power fastener driver of  FIG. 23 , illustrating the nosepiece of the power fastener driver. 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a powered fastener driver  10  (e.g., a cable stapler) for driving fasteners  12  (e.g., staples of a staple collation) held within a magazine  14  into a workpiece. The driver  10  includes a nosepiece  18  that sequentially receives the fasteners from the magazine  14  prior to each fastener-driving operation. The nosepiece  18  includes a contact trip  20  that allows the driver  10  to be operated in a single shot mode. In some embodiments of the driver  10 , the contact trip  20  may permit operation in the single shot mode and/or a bump or continuous shot mode. The driver  10  includes a housing  22  defining a head portion  26 , a handle portion  30 , and a battery receptacle portion  34  that receives a battery pack  38 . In the illustrated embodiment, the housing  22  is longitudinally split at a parting line  24  into first and second housing portions. The driver  10  further includes a belt clip  40  secured to the housing  22  adjacent the battery receptacle  34 . 
     With reference to  FIG. 2 , the driver  10  includes a trigger  42  that selectively provides power to a drive mechanism  46  enclosed within the handle portion  30  of the driver  10 . The drive mechanism  46  includes an electric motor  50 , a gear box  54  that receives torque from the motor  50 , and an output shaft  56  driven by the gear box  54 . In some embodiment, the motor  50  is a brushed DC motor that receives power from the battery pack  38 . In some embodiments of the driver  10 , the motor  50  may be configured as a brushless direct current (DC) motor. 
     The powered fastener driver  10  includes a firing mechanism  62  within the head portion  26  of the housing  22 . The firing mechanism  62  is coupled to the drive mechanism  46  and is operable to perform a fastener driving operation. The firing mechanism  62  includes a movable member (e.g., a piston  66 ) for reciprocal movement within the head portion  26 , a biasing member (e.g., one or more compression springs  70 ,  72 ) seated against the piston  66 , and a driver blade  74  attached to the piston  66  ( FIG. 4 ). The biasing member  70  urges the piston  66  and the driver blade  74  within the head portion  26  towards a driven or bottom-dead center (BDC) position to drive the fastener  12  into the workpiece. In the illustrated embodiment, the biasing member includes a nested pair of compression springs  70 ,  72  that act in unison to urge the piston  66  and the driver blade  74  towards the BDC position. 
     A lifter assembly  58  is positioned between the drive mechanism  46  and the firing mechanism  62  and is operated by the drive mechanism  46  to return the piston  66  and the driver blade  74  towards a top-dead center (TDC) position, against the bias of the biasing member  70 . During a driving cycle, the biasing member  70  of the firing mechanism  62  urges the driver blade  74  and piston  66  from the TDC position towards the BDC position to fire a fastener into the workpiece. The lifter assembly  58 , which is driven by the drive mechanism  46 , is operable to move the piston  66  and the driver blade  74  from the BDC position toward the TDC position, stopping short of the TDC position at an intermediate ready position, so the firing mechanism  62  is ready for a subsequent fastener driving operation. 
     Now with reference to  FIGS. 2 and 3 , the driver  10  further includes a primary guide member (e.g., primary guide post  80 ) that slidably supports the piston  66  and a secondary guide member (e.g., secondary post  82 ), which slidably supports a bracket  86  coupled for movement with the piston  66 , spaced from the primary guide post  80 . The secondary post  82  is positioned between the primary guide post  80  and the lifter assembly  58  and is configured to slidably support the bracket  86 . Because in the illustrated embodiment the piston  66  and the bracket  86  are integrally formed as a single piece, both of the primary and secondary guide posts  80 ,  82  slidably support the piston  66 . In the illustrated embodiment, a primary guide axis  90  extends centrally through the primary guide post  80  and a secondary guide axis  94  extends centrally through the secondary post  82 . The primary guide axis  90 , the secondary guide axis  94 , and the drive axis  78  are oriented parallel with each other and are each transverse to the motor axis  76 . The primary and secondary guide posts  80 ,  82  are each cylindrical posts define guide surfaces that are devoid of any threads so the piston  66  can freely move along the primary and secondary guide posts  80 ,  82  in response to rotation of the lifter assembly  58   
     Now with reference to  FIG. 4 , the lifter assembly  58  and the piston  66  is illustrated in detail. The piston  66  defines a first bore  116  that is sized to receive and support the primary guide post  80  ( FIG. 3 ) along the primary guide axis  90 , a second bore  120  formed in the bracket  86 , which is sized to receive and support the secondary guide post  82  ( FIG. 3 ) along the secondary guide axis  94 , and a cavity  124  surrounding the first bore  116  and sized to receive the biasing member  70  ( FIG. 3 ). In the illustrated embodiment, the bracket  86  is integrally formed with the piston  66 . In other embodiments, the bracket  86  may be formed separate from the piston  66  and may be coupled to the piston  66 . 
     The bracket  86  includes a first protrusion  98  and a second protrusion  102  vertically spaced from the first protrusion  98  along the axis  94 . The first and second protrusions  98 ,  102  each extend towards the lifter assembly  58 . In the illustrated embodiment, the first protrusion  98  extends further from the bracket  86  (e.g., towards the lifter assembly  58 ) than the second protrusion  102 . In other words, the first protrusion  98  is longer than the second protrusion  102 . The lifter assembly  58  includes a first eccentric pin  104  and a second eccentric pin  108  that selectively engage with a corresponding one of the first and second protrusions  98 ,  102  formed on the bracket  86  of the piston  66 . In the illustrated embodiment, the second eccentric pin  108  extends further from the lifter assembly  58  (e.g., towards the bracket  86 ) than the first eccentric pin  104  so the second eccentric pin  108  is sized to engage with the second protrusion  102 . In other words, the second eccentric pin  108  is longer than the first eccentric pin  104 . The construction of the lifter assembly  58  and the bracket  86  displaces the piston  66  and the driver blade  74  from the BDC position toward the TDC position during a single fastener driving cycle. Because the secondary guide member  82  is positioned adjacent and in close proximity to the lifter assembly  58  (e.g., in the bore  120 ), the physical deflection of the bracket  86 , and thus the amount of bending stress experienced by the bracket  86 , is reduced when the lifter assembly  58  moves the piston towards the TDC position. 
     With continued reference to  FIGS. 2 and 3 , the fastener driver  10  includes a frame  112  coupled to the housing  22  for supporting the lifter assembly  58  and a first end of each of the primary and secondary guide posts  80 ,  82 . The frame  112  also defines a housing, which is a component of the gear box  54 , in which a gear train (not shown) is located. In other words, the gear box  54  is integrally formed on the frame  112 . The output shaft  56  extends through an aperture in the frame  112  with the lifter assembly  58  located adjacent and in close proximity to a vertical face of the frame  112  oriented perpendicular to the axis  76 . An end cap  114  within the housing  22  supports an opposite, second end of each of the primary and secondary guide posts  80 ,  82 . The end cap  114  includes a seat  115  ( FIG. 3 ) against which a top end of the spring  70  is seated. The frame  112  is constructed as a single member, which supports the lifter assembly  58 , while allowing rotatable movement of the lifter assembly  58 , and rigidly supports the primary and secondary guide posts  80 ,  82  within the housing  22 . In the illustrated embodiment, the frame  112  has a first portion positioned within the head portion  26  of the housing  22  and a second portion positioned within the handle portion  30 . The construction of the frame  112  allows the firing mechanism  62  and the drive mechanism  46  to be assembled separately (e.g., as shown in  FIG. 3 ) and inserted within the housing  22 . As a result, this allows for a more compact arrangement of the firing mechanism  62  and the drive mechanism  46 , which reduces the overall size of the driver  10 . 
     Now with reference to  FIG. 2 , the powered fastener driver  10  includes a length L defined between a front end of driver  10  (e.g., a front end of the contact trip  20 ) and a rear end of the housing  22  (e.g., the head portion  26 ). The length L of the driver  10  is less than or equal to 18 centimeters. In the illustrated embodiment, the length L is 16.5 centimeters. In some embodiments, the length L may be in a range from 12.5 centimeters to 18 centimeters. In some embodiments, the length L may be in a range from 12.5 centimeters to 16.5 centimeters. 
     Now with reference to  FIGS. 5 and 6 , the lifter assembly  58  includes an outer circumferential surface  130 . Each of the eccentric pins  104 ,  108  are arranged proximate the outer circumferential surface  130 . In addition, the first eccentric pin  104  is positioned at a first radial distance R 1  relative to a rotational axis of the lifter assembly  58  (i.e., the motor axis  76 ). The second eccentric pin  108  is positioned at a second radial distance R 2  that is less than the first radial distance R 1  of the first eccentric drive pin  104 . As such, the eccentric pins  104 ,  108  of the lifter assembly  58  are positioned at different radial distances R 1 , R 2  relative to the axis  76 . In other words, the eccentric pins  104 ,  108  are radially offset with respect to each other. 
     Now with reference to  FIG. 2 , when the piston  66  is moved from the bottom-dead-center (BDC) position to the top-dead-center (TDC) position, the lifter assembly  58  rotates so the second eccentric pin  108  engages the second protrusion  102  of the bracket  86  of the piston  66 . Because the second eccentric pin  108  is positioned at the smaller, second radial distance R 2  than the first eccentric pin  104 , less reaction torque is applied on the motor  50  by the spring  70  when the piston  66  is stationary in the ready position between the BDC and TDC positions. Additionally, because the first eccentric pin  104  is shorter than the second eccentric pin  108 , during rotation of the lifter assembly  58 , only the second eccentric pin  108  is capable of engaging the second protrusion  102 . In other words, the first eccentric pin  104  has a first height and the second eccentric pin has a second height that is larger than the first height. 
     For example, the lifter assembly  58  is driven to rotate in a first direction by the drive mechanism  46  so the first and second eccentric pins  104 ,  108  engage the first and second protrusions  98 ,  102  in sequence, which returns the piston  66  and the driver blade  74  from the BDC position toward the TDC position. Since the radius R 2  of the second eccentric pin  108  is smaller than the radius R 1  of the first eccentric pin  104 , the second eccentric pin  108  has a lower linear velocity than the linear velocity of the first eccentric pin  104  when the lifter assembly  58  is rotated by the motor  50 . As a result, the higher linear velocity of the first eccentric pin  104  increases firing speeds by returning the piston  66  to the TDC position faster while the lower linear velocity of the second eccentric pin  108  reduces the reaction torque on the motor  50 . 
     In operation, at the conclusion of a first drive cycle, the motor  50  rotates the output shaft  56 , and therefore the lifter assembly  58 , about a motor axis  76  to drive the piston  66  and the driver blade  74  toward the TDC position, compressing the biasing member  70 . Prior to reaching the TDC position, the motor  50  is deactivated and the piston  66  and the driver blade  74  are held in a ready position, which is located between the TDC and the BDC positions, concluding a first drive cycle. When trigger  42  is actuated to initiate a subsequent, second drive cycle, the lifter assembly  58  is again rotated by the motor  50 , which releases the biasing member  70  and drives the piston  66  and the driver blade  74  toward the BDC position, which causes the driver blade  74  to move about a drive axis  78  and thereby driving the fastener  12  into the workpiece. Following the release of the biasing member  70 , the lifter assembly  58  returns the piston  66  towards the TDC position in preparation for another subsequent drive cycle. 
     Now with reference to  FIGS. 7-11 , the magazine  14  includes an outer magazine cover  132  and an inner magazine body  136  received within the outer magazine cover  132 . The inner magazine body  136  is slidable relative to the outer magazine cover  132  between a first, closed position ( FIG. 7 ), and a second, open position ( FIG. 8 ). The magazine  14  includes a top surface  140 , which is secured to the driver ( FIG. 1 ), and a bottom surface  144  that engages the workpiece and is opposite the top surface  140 . The outer magazine cover  132  includes a first, front portion  148  adjacent the nosepiece  18  ( FIG. 1 ), and a second, rear portion  152  adjacent the battery receptacle  34 . The inner magazine body  136  includes a front portion  150  and a rear portion  154  opposite the front portion  148 . For example, when the magazine  14  is in the closed position, the inner magazine body  136  is positioned entirely within an interior cavity defined by the outer magazine cover  132  so the front portion  150  and the rear portion  154  of the inner magazine body  136  respectively aligns with the front portion  148  and the rear portion  152  of the outer magazine cover  132 . The magazine  14 , therefore, has a length extending along a longitudinal axis  138  between the front and rear portions  148 ,  152  of the outer magazine cover  132 . When the inner magazine body  136  is moved towards the open position, the inner magazine body  136  slides (to the right from the reference of frame of  FIG. 7  and to the left from the frame of reference of  FIG. 8 ) until the front portion  150  of the inner magazine body  136  is positioned proximate the rear portion  152  of the outer magazine cover  132 . The magazine  14  has a length extending along the longitudinal axis  138  between the front portion  148  of the outer magazine cover  132  and a rear portion  154  of the inner magazine body  136 . 
     A lock assembly  156  is positioned at the rear portion  152  of the inner magazine body  136 . The lock assembly  156  includes a flange portion  160  ( FIG. 11 ) positioned within the inner magazine body  136 , which secures the lock assembly  156  to the inner magazine body  136 . The lock assembly  156  is configured to selectively couple the inner magazine body  136  to the outer magazine cover  132  to maintain the inner magazine body  136  in the closed position. In the illustrated embodiment, a latching bracket  164  is coupled to the outer magazine cover  132  adjacent the rear portion  152  of the magazine  14  and a latching recess  168  ( FIG. 10 ) is formed in a side surface of the outer magazine cover  132 . 
     The lock assembly  156  includes a latch member  170  that selectively engages the latching bracket  164  and is seated within the latching recess  168  when the outer magazine cover is in the closed position ( FIG. 7 ). In the illustrated embodiment, the latch member  170  is biased (e.g., via a spring) towards a closed or latched position. In order to move the inner magazine body  136  towards the open position, the latch member  170  is actuated, releasing the latching bracket  164  to permit the inner magazine body  136  to be extended from the outer magazine cover  132  towards the open position ( FIG. 8 ). In the open position, the operator may load fasteners into the magazine  14 . 
     With reference to  FIGS. 8 and 9 , the inner magazine body  136  includes an extruded rail  172  defining the fastener channel  176  in which the staples  12  are received ( FIG. 1 ). In the illustrated embodiment, the fastener channel  176  has a U-shape (represented by the broken lines in  FIG. 9 ) corresponding to the U-shape of the staples  12 . In the illustrated embodiment, the rail  172  is formed as two separate extrusions that define an edge portion  180  and two opposed sidewalls  184  adjacent the edge portion  180 . Each of the staples  12  is configured to straddle the edge portion  180  and the sidewalls  184  of the rail  172  when the staples  12  are received in the fastener channel  176 . In other embodiments, the extruded rail  172  may be formed as a single extruded structure. The outer magazine cover  132  further includes a pair of side surfaces  182  and a slot  186  recessed in the side surfaces  182 . The slot  186  receives the inner magazine body  136  so the inner magazine body  136  can slide relative to the outer magazine cover  132 . 
     Now with reference to  FIGS. 11-13 , the magazine  14  further includes a pusher body  188  ( FIGS. 12, and 13 ) positioned within the fastener channel  176  of the magazine  14  and a latch  196  ( FIG. 11 ) coupled to the top surface  140  of the outer magazine cover  132 . The pusher body  188  is slidably coupled to the magazine  14  and biases the collated fastener strip toward the front portion  148  of the magazine  14 . In the illustrated embodiment, the magazine  14  includes a biasing member (e.g., roll coil spring  192 ;  FIG. 12 ) configured to bias the pusher body  188  toward the front portion  148  of the magazine  14  (i.e., toward the nosepiece  18 ). 
     The latch  196  includes a latch projection  216  that is received within an opening  204  defined in the top surface  140  of the outer magazine cover  132  and first and second projections  208 ,  212  oriented on each side of the latch  196 . The latch projection  216  is biased inward toward the flange portion  160  of the lock assembly  156  (e.g., downward from the frame of reference of  FIG. 10 ) through the opening  204 . The latch projections  216  each define a contact surface  240 . The contact surface  240  defines a first plane  244  oriented at an oblique angle A 1  relative to a vertical reference plane  242  that is perpendicular to the longitudinal axis  138  of the magazine  14 . The opposing side of arms  208 ,  212  define arcuate segments  238  opposing the contact surface  240 . In the illustrated embodiment, the angle A 1  is an acute angle (e.g., less than 90 degrees). In some embodiments, the angle A 1  is in a range from 10 degrees to 30 degrees. In some embodiments, the angle A 1  is approximately 15 degrees. 
     The pusher body  188  that is configured to straddle the edge portion  180  and the sidewalls  184  of the rail  172 . The pusher body  220  defines a main body  224  that supports the biasing member  192  and first and second arm members  230 ,  232 . Each arm member  230 ,  232  includes a contact surface  236  ( FIG. 13 ) configured to contact the contact surface  240  ( FIGS. 12 and 13 ) of the first and second projections  208 ,  212 , respectively, of the latch  196 . The pusher body  220  is selectively engageable with the latch  196  for maintaining the pusher body  220  in a latched position (e.g., for loading). In the illustrated embodiment, the contact surfaces  236  are each curvilinear and include a constant radius R 1 . As a result, a single line of contact (e.g., extending along the longitudinal axis  138  of the magazine  14 ) is formed between the contact surface  236  of the pusher body  188  (e.g., at the radius R 1 ) and the contact surface  240  of the latch  196 . 
     When the magazine  14  is moved towards a closed position, the pusher body  188  is automatically adjusted from the latched position to a released position by engagement between the flange portion  160  of the lock assembly  156  and the latch projection  216  of the latch  196  when the inner magazine body  136  is slid toward the closed position. For example, the translation of the flange portion  160  in the closing direction of the inner magazine body  136  causes the latch projection  216  to slide upward along an inclined face of the flange portion  160 , which deflects the latch  196  upward (e.g. from the frame of reference of  FIGS. 10 and 12 ). As a result, the contact surface  240  of the latch  196  is moved above the contact surface  236  of the pusher body  188 , which releases the pusher body  188  to bias the collated strip of staples towards the nosepiece  18 . 
     When the magazine is moved towards an open position, the user releases the lock assembly  156  and slides the inner magazine body  136  ( FIG. 8 ) and the pusher body  188  relative to the outer magazine cover  132 . The movement of the pusher body  188  causes the arcuate members  238  ( FIG. 12 ) of the first and second arm members  230 ,  232  of the latch  196  to engage with the arm members  208 ,  212  of the pusher body  188 , which causes the latch  196  to deflect upwards (with reference to  FIG. 12 ) so the arm members  208 ,  212  of the latch  196  move beyond (e.g., underneath) the arm members  208 ,  212  of the pusher body  188 . Once the arm members  208 ,  212  of the latch  196  are beyond the arm members  230 ,  232  of the pusher body  188 , the latch  196  is urged towards the position shown in  FIG. 12  (e.g. so the contact surfaces  236 ,  240  are adjacent each other). Once the user releases the inner magazine body  136 , the biasing member  192  urges the pusher body  188  forward (e.g., towards the front portion  148  of the outer magazine cover  132 ), which causes the contact surface  236  of each arm member  230 ,  232  of the pusher body  188  to engage the contact surface  240  of the latch  196 . Thereby, the pusher body  188  is maintained in the latched position against the bias of the biasing member  192 . The user may now load fasteners into the fastener channel  176  of the magazine  14  in front of the pusher body  188 . The user may then load the collated strip of staples  12  in the magazine  14  in front of the pusher body  188 . To adjust the pusher body  188  from the latched state into the normal operating state, the user pushes the inner magazine body  136  towards the closed position ( FIG. 7 ), which disengages the engagement between the contact surfaces  236 ,  240  as described above. As a result, the pusher body  188  is released and biases the collated strip of staples  12  towards the nosepiece  18 . 
       FIGS. 14-17  illustrate a magazine  314  according to another embodiment of the invention. The magazine  314  is like the magazine  14  shown in  FIG. 7-11  and described above. Therefore, like features are identified with like reference numerals plus “300”, and only the differences between the two will be discussed. 
     The magazine  314  includes an outer magazine cover  432  and an inner magazine body  436  received within and slidable relative to the outer magazine cover  432  between a first closed position ( FIG. 14 ) and a second, open position ( FIG. 15 ). The outer magazine cover  432  includes a first, front end  448  adjacent the nosepiece  18  ( FIG. 1 ), a second, rear end  452  adjacent the battery receptacle  34  ( FIG. 1 ), and a length L extending along a longitudinal axis  438  between the front end  448  and the rear end  452 . A lock assembly  456  is positioned at a rear end  454  of the inner magazine body  436  to selectively couple the inner magazine body  436  to the outer magazine cover  432  to maintain the inner magazine body  436  in the closed position. The magazine  314  further includes a pusher body  488  ( FIG. 14 ) positioned within a fastener channel  476  ( FIG. 17 ) of the magazine  314  and a latch  496  ( FIG. 14 ) coupled to a top wall  440  of the outer magazine cover  432 . The pusher body  488  is slidably coupled to the magazine body  436  and biases one or more collated fastener strips  312  toward the front end  448  of the magazine cover  432 . The outer magazine cover  432  further includes a pair of parallel side walls  482  extending from opposite sides of the top wall  440  and a slot  486  within each of the side walls  482  in which the inner magazine body  436  is received so the inner magazine body  436  can slide relative to the outer magazine cover  432 . 
     Now with reference to  FIGS. 15-17 , the outer magazine cover  432  includes an internal rib  513  and an external rib  515 , which each extending inward from each of the side walls  482  of the outer magazine cover  432 . The internal and external ribs  513 ,  515  are parallel and vertically spaced on each side of the slot  486  ( FIG. 17 ). In the illustrated embodiment, the internal rib  513  and the external rib  515  each extend a length L 1  ( FIG. 15 ) of the outer magazine cover  432 , which is a portion of the total length L of the outer magazine cover  432 . The fastener channel  476  defines a width W 1  that is sized receive the collated fastener strips  312  and the internal and external ribs  513 ,  515  define a gap therebetween having a width W 2  that is less than the width W 1  of the fastener channel  476  ( FIG. 17 ). Therefore, the internal and external ribs  513 ,  515  reduce the width W 2  of the opening formed at the bottom of the outer magazine cover  432  to restrict the collated fastener strips  312  from being removed from and/or installed into the fastener channel  476 . In some embodiments of the magazine  314 , the length L 1  of the internal and external ribs  513 ,  515  may be equal to or greater than a length of a single collated fastener strip  312  to restrict removal of the collated fastener strip  312  when located within the length L 1  of the magazine cover  432 . 
     In the illustrated embodiment, the lengths L 1  of the internal and external ribs  513 ,  515  are approximately equal. In other embodiments, the length of the external ribs  515  may be greater than or less than the length of the internal ribs  513 . In other embodiments, the outer magazine cover  432  may only include one of either the internal ribs  513  or the outer ribs  515 . While the illustrated internal and external ribs  513 ,  515  are continuous structures, it should be appreciated that the ribs may alternatively be segmented or discontinuous structures. 
     A second length L 2  of the outer magazine cover  432  is devoid of the internal and external ribs  513 ,  515  and defines an installation region where the collation fastener strips  312  can be individually inserted when the magazine body  436  is in the open position ( FIG. 15 ). The length L 2  may be equal to or greater than the length of a single collated fastener strip  312 , which requires the magazine body  436  to be fully retracted to its open position, thereby securing the pusher body  488  to the latch  496  as described above, prior to installation of a new collated fastener strip  312 . 
     When the collated fastener strips  312  are inserted within the magazine  314 , a first collated fastener strip  312  is inserted within the installation region of the outer magazine cover  432  and moved towards the front end  448  of the outer magazine cover  432 . A second collated fastener strip  312  is then inserted within the installation region of the outer magazine cover  432 . The inner magazine body  436  is moved towards the closed position ( FIG. 14 ), which releases the pusher body  488  and biases the collated fastener strips  312  towards the nosepiece  18 . As the pusher body  488  biases the collated fastener strips  312 , the internal ribs  513  supports the tips of the collated fastener strips  312 . The inner ribs  513  prevent the adjacent strips  312  from buckling, ensures proper alignment of the fastener strips  312  within the magazine  314 , and supports the tips of the fastener strips  312  when the fasteners are sequentially fed from the magazine  14  into the nosepiece  18  ( FIG. 1 ) prior to each fastener-driving operation. 
     The magazine  614  includes an outer magazine cover  732  and an inner magazine body  736  received within the outer magazine cover  732 . The inner magazine body  736  is movable between a first closed position ( FIG. 18 ), a second, intermediate position ( FIG. 20 ), and a third, open position ( FIGS. 19 and 21 ). The outer magazine cover  732  includes a first, front end  748  adjacent a nosepiece  618 , second, rear end  752  adjacent the battery receptacle  634 . The inner magazine body  736  includes a front end  750  and a rear end  754  opposite the front end  748 . In the open position, collated fastener strips  312  can be inserted through an installation region  807  formed in the rear end  752  of the outer magazine cover  732 . The magazine  614  further includes a pusher body  788  ( FIG. 21 ) positioned within a fastener channel  776  of the magazine  614 , which is slidably coupled to the magazine body  736  and biases collated fastener strips  612  toward a front end  748  of the magazine cover  732 . 
     A lock assembly  756  is positioned at a rear end  754  of the inner magazine body  736  to selectively couple the inner magazine body  736  to the outer magazine cover  732  to maintain the inner magazine body  736  in the closed position ( FIG. 18 ). The lock assembly  756  includes a latch member  770  that selectively engages the latching bracket  764  and is seated within the latching recess  768  when the outer magazine cover  732  is in the closed position ( FIG. 18 ). The latching bracket  764  further defines a recess  809  that is sized to receive a protrusion  811  formed on the inner magazine body  736  when the magazine  614  is in the second, intermediate position ( FIG. 20 ). 
     Now with reference to  FIGS. 20-22 , the outer magazine cover  732  includes a rib  815  that extends inward from each of the side walls  782  of the outer magazine cover  732 . The fastener channel  776  defines a width W 1  ( FIG. 22 ) that is sized receive the collated fastener strips  612  and the ribs  815  define a gap therebetween having a width W 2  that is less than the width W 1  of the fastener channel  776 . Therefore, the ribs  815  prevent installation of the collated fastener strips  612  through the bottom of the outer magazine cover  732 , thus requiring the collated fastener strips  612  to be installed through the installation region  807  at the rear end  752  of the magazine cover  732 .   
     To insert a collated fastener strip  612  into the magazine  614 , the latch member  770  of the lock assembly  756  is actuated to permit slidable movement of the inner magazine body  736  relative to the outer magazine cover  732 . Once the inner magazine body  736  reaches the second, intermediate position ( FIG. 20 ), the protrusion  811  on the inner magazine body  736  engages the recess  809  formed in the latching bracket  764  so the inner magazine body  736  can pivot relative to the outer magazine cover  732  towards the third, open position ( FIG. 21 ). In the open position, the collated fastener strips  612  can be inserted within the magazine  614  through the installation region  807  formed in the rear end  752  of the outer magazine cover  732  and moved towards the front portion  748  of the outer magazine cover  732 . Once the collated fastener strips  612  are inserted within the outer magazine cover  732 , the inner magazine body  736  is pivoted back to the second, intermediate position and then is slidably moved towards the closed position ( FIG. 18 ), which releases the pusher body  788  as described above and biases the collated fastener strips  612  towards the nosepiece  618 . 
       FIG. 23  illustrates a power fastener driver  1010  according to another embodiment of the invention. The power fastener driver  1010  is like the power fastener driver  10  shown in  FIG. 1-13  and described above. Therefore, like features are identified with like reference numerals plus “1000”, and only the differences between the two will be discussed. 
     The powered fastener driver  1010  (e.g., a cable stapler) includes a magazine  1014  that holds fasteners  1012  (e.g., staples of a staple collation) and a nosepiece  1018  that sequentially receives the fasteners  1012  from the magazine  1014  prior to each fastener-driving operation. The driver  1010  includes a trigger  1042  that selectively activates a drive mechanism  1046  enclosed within a handle portion  1030  of the driver  1010 . The drive mechanism  1046  includes an electric motor  1050  and a gear box  1054  that receives torque from the motor  1050 . A lifter assembly  1058  is coupled to the drive mechanism  1046  and is positioned between the drive mechanism  1046  and a firing mechanism  1062 . 
     The firing mechanism  1062  includes a movable member (e.g., a piston  1066 ) for reciprocal movement within the head portion  1026 , a biasing member (e.g., a compression spring  1070 ) seated against the piston  1066 , and a driver blade  1074  attached to the piston  1066 . The biasing member  1070 ,  1072  urges the piston  1066  and the driver blade  1074  within the head portion  1026  towards a driven or bottom-dead center (BDC) position to drive the fastener  1012  into the workpiece. 
     The lifter assembly  1058  is operated by the drive mechanism  1046  to return the piston  1066  and the driver blade  1074  towards a top-dead center (TDC) position, against the bias of the biasing member  1070 ,  1072 . In the illustrated embodiment, the biasing member includes a nested pair of compression springs  1070 ,  1072  that act in unison to urge the piston  1066  and the driver blade  1074  towards the BDC position. The compression springs  1070 ,  1072  include a first end supported within the piston  1066  and a second end supported within an end cap  1114 . The end cap  1114  includes a first, outer recess  1117  and a second, inner recess  1119  that is surrounded by the first recess  1117 . A first, outer washer  1121  is supported within the first recess  1117  formed in the end cap  1114 . A second, inner washer  1123  is supported within the second recess  1119  formed in the end cap  1114 . The end cap  1114  further includes an outer spring sleeve  1125  that retains the first washer  1123  within the end cap  1114 . The first washer  1123  is positioned between the second end of the first compression spring  1070  and the end cap  1114 . The second washer  1125  is positioned between the second end of the second compression spring  1072  and the end cap  1114 . In the illustrated embodiment, the spring sleeve  1125  is formed of a metallic material (e.g., steel) and the washers  1121 ,  1123  are formed of a plastic material. The spring sleeve  1123  reduces deformation of the outer washer  1117  and helps maintain the shape of the washer  1117 . 
     Further, the compression springs  1070 ,  1072  are formed of a metallic material such as 55CrSi. The first, outer compression spring  1070  has a first wire thickness T 1  and the second, inner compression spring has a second wire thickness T 2  that is less than the first wire thickness T 1 . The outer compression spring  1070  includes an outer nominal diameter of 40 millimeters, an uncompressed length of 93 millimeters, and a stiffness of 8.7 N/mm. In some embodiments, the outer nominal diameter of the outer compression spring  1070  may be in a range from 30 millimeters to 50 millimeters. In some embodiments, the stiffness of the outer compression spring  1070  may be in a range from 8.0 N/mm to 10 N/mm. The inner compression spring  1072  includes an outer nominal diameter of 25 mm, an uncompressed length of 93 millimeters, and a stiffness of 4.35 N/mm. In some embodiments, the outer nominal diameter of the inner compression spring  1072  may be in a range from 30 millimeters to 50 millimeters. In some embodiments, the stiffness of the inner compression spring  1072  may be in a range from 3.0 N/mm to 6.0 N/mm. In some embodiments, the uncompressed length of the inner and outer compression springs  1070 ,  1072  may be in a range from 70 millimeters to 110 millimeters. 
     As shown in  FIG. 25 , the lifter assembly  1058  is formed as a unitary body having an input shaft  1056 , which may also be considered an output shaft of the gear box  1054 , and a hub  1013  that selectively engages a portion of the firing mechanism  1062  to return the piston  1066  and the driver blade  1074  towards the TDC position. In the TDC position, the compression springs  1070 ,  1072  store at least 14.5 Joules (J) of potential energy, which provides sufficient energy to fully seat fasteners into a workpiece. The fastener driver  1010  is able to store at least 14.5 J of potential energy, with an overall length L defined between a front end of driver  1010  (e.g., a front end of the contact trip  1020 ) and a rear end of the housing  1022  (e.g., the head portion  1026 ) of 18 centimeters or less, and in some embodiments 16.5 centimeters or less, because of the nested springs  1070 ,  1072  acting on the piston  1066 . By nesting dual springs  1070 ,  1072  having different stiffnesses, more potential energy can be stored in the driver  1010  compared to a single spring within the same spatial confines. In other words, to achieve an equivalent potential energy with a single compression spring, such a spring would necessarily require a longer uncompressed length to accommodate a greater amount of compression, which then requires the driver to have a greater overall length (i.e., greater than 18 centimeters). With an overall length of 18 centimeters or less, the driver  1010  can be used in more confined spaces compared to prior art fastener drivers with an overall length of greater than 18 centimeters. 
     For example, the hub  1013  may include eccentric pins  1104 ,  1008  that engage respective first and second protrusions  1098 ,  1102  ( FIG. 24 ) of the firing mechanism, which return the piston  1066  and the driver blade  1074  from the BDC position toward the TDC position. In the illustrated embodiment, the eccentric pins  1104 ,  1108  are secured within recesses  1017  ( FIG. 25 ) formed in the hub  1013  of the lifter assembly  1058 . In other embodiments, the eccentric pins  1104 ,  1108  may be integrally formed with the hub  1013 . 
     The unitary construction of the lifter assembly  1058  increases performance and durability of the lifter assembly  1058  by reducing the number of separate assembled parts in the lifter assembly  1058 . In the illustrated embodiment, the lifter assembly  1058  is formed by forging a piece of raw material (e.g., steel, aluminum, etc.) into the desired form. The recesses  1017  may be formed by machining the lifter assembly  1058  after the forging process is completed. In other embodiments, the eccentric pins  1104 ,  1108  may also be formed as part of the unitary body of the lifter assembly  1058  during the forging process. 
     Now with reference to  FIG. 26 , the magazine  1014  is sized to receive a collated fastener strip having a plurality of fasteners  1012 . Each of the fasteners  1012  includes a crown section  1021  and a tip  1025  opposing the crown section  1021 . The fasteners  1012  are held in the collated fastener strip by collation tabs  1029  interconnecting the crown sections  1021  of the fasteners  1012 . The nosepiece  1018  defines a fastener driving channel  1031  from which consecutive fasteners  1012  provided from the magazine  1014  are driven during each fastener driving operation. 
     The powered fastener driver  1010  may include a fastener alignment mechanism that urges the fastener  1012  adjacent the fastener driving channel  1031  of the nosepiece  1018  towards a loading position. In the illustrated embodiment, the alignment mechanism may include a magnetic element  1033  positioned adjacent a first, front portion  1150  of the magazine  1014  and the nosepiece  1018  of the driver  1010 . In the illustrated embodiment, the magnetic element  1033  is positioned proximate a tip  1025  of the fastener  1012  adjacent the fastener driving channel  1031  of the nosepiece  1018 . The magnetic element  1033  produces a magnetic force that interacts with and urges the tip  1025  of the fastener  1012  upwards from the frame of reference of  FIG. 26  (i.e., towards the nosepiece  1018 ). The use of the magnetic element  1033  aligns the fastener  1012  with the fastener driving channel  1031  without increasing resistance during the fastener driving operation. In other embodiments, the magnetic element  1033  may be positioned adjacent other sections of the fastener  1012 . Additionally, or alternatively, one or more magnetic elements  1033  may be used to ensure alignment and upward bias of the fastener  1012 . 
     During a fastener driving event, the collation tab  1029  of the fastener  1012  positioned adjacent the fastener driving channel  1031  may break off from the adjacent collation tab, which may cause rotation of the fastener  1012 . The magnetic force provided by the magnetic element  1033  counteracts the rotation caused during the breaking process of the collation tab  1029  to resist over-rotation of the fastener  1012  within the magazine  1014  (e.g., beyond the loading position) and ensures proper alignment between the fastener  1012  and the fastener driving channel  1031  prior to the fastener  1012  entering the channel  1031 . In the illustrated embodiment, a fastener axis  1035  extends centrally through the fastener  1012 . When the fastener  1012  is in the loading position (illustrated by a broken line outline of the fastener  1012 ), the tip  1025  of the fastener  1012  may be urged upwards (e.g., to pre-tilt the fastener  1012 ) by the magnetic element  1033 , which causes a fastener axis  1035 ′ to be non-parallel with a drive axis  1078  defined by the driver blade  1074 . As the collation tab  1029  breaks, the fastener  1012  is rotated to realign the fastener axis  1035 ′ with the fastener axis  1035  to become parallel with the drive axis  1078  defined by the driver blade  1074 . 
     Now with reference to  FIG. 27 , the nosepiece  1018  of the powered fastener driver  1010  includes an interior surface  1039  sized to receive a cable being secured to a workpiece during a fastener driving operation. In the illustrated embodiment, the interior surface  1039  includes a first portion  1043  having a first width W 1  and a second portion  1047  having a second width W 2  that is greater than the first width W 1 . In other words, the interior surface  1039  is stepped to accommodate different diameter cables during the fastener driving operation. In some embodiments, the second portion  1047  may be movable relative to the first portion  1043  to adjust the width of the second portion  1047  of the nosepiece  1018  to accommodate larger diameter cables. In the illustrated embodiment, the first portion of the nosepiece has a width of 15.5 millimeters and the second portion of the nosepiece has a width of 16.5 millimeters. 
     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described. 
     Various features of the invention are set forth in the following claims.