Abstract:
There is proposed a nail driving tool provided with a driver guide including an injection hole for driving a nail and a contact arm surrounding an outer surface of a forward end of the driver guide in a nail driving direction, provided with an eject hole penetrating through the contact arm, movable on an axial line along the nail driving direction for making triggering operation for driving a nail effective by being moved in the opposite direction to the nail driving direction and designed to drive a nail outwardly through the eject hole, wherein a diameter of an outer surface of a forward end portion of the contact arm is decreased taperingly toward its edge in the nail driving direction. A diameter of the eject hole of the contact arm in the vicinity of the forward end of the contact arm in the nail driving direction is nearly equal to that of the injection hole of the driver guide in the vicinity of the forward end of the driver guide in the nail driving direction and an outer diameter of the contact arm in the vicinity of the forward end of the contact arm is equal to or smaller than an outer diameter of the driver guide in the vicinity of the forward end of the driver guide. A spike is provided on the outer surface of the forward end portion of the contact arm for preventing slippage of the contact arm when a nail is driven obliquely. It is easy for the user of the nail driving tool to see and aim at the point to drive a nail.

Description:
FIELD OF THE INVENTION 
     The invention relates to a nail driving tool. 
     BACKGROUND OF THE INVENTION 
     Heretofore, for example, as shown in Publication of Unexamined Japanese Utility Model Application No, 2-51079, there is known a nail driving tool provided with a driver guide having an injection hole for driving a nail and a contact arm surrounding an outer surface of a forward end of the driver guide in a nail driving direction, movable on an axial line along the nail driving direction, for making triggering operation for driving a nail effective by being moved in the opposite direction to the nail driving direction. 
     However, it is difficult for the user of such a conventional nail driving tool to see and aim at the point for driving a nail, since a size of a forward end portion of the contact arm in the nail driving direction is large. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a nail driving tool by which the user can easily see and aim at the point for driving a nail. 
     The object of the invention is attained by providing a nail driving tool provided with a driver guide including an injection hole for driving a nail and a contact arm surrounding an outer surface of a forward end of the driver guide in a nail driving direction, provided with an eject hole penetrating through the contact arm along the nail driving direction and movable on an axial line along the nail driving direction, for making triggering operation for driving a nail by being moved in the opposite direction to the nail driving direction, wherein a diameter of an outer surface of the contact arm is decreased taperingly toward its edge in the nail driving direction. 
     The diameter of the outer surface of the contact arm in the vicinity of the forward end of the contact arm in the nail driving direction may be preferably equal to or smaller than a diameter of an outer surface of the driver guide in the vicinity of the forward end of the driver guide in the nail driving direction. 
     According to the nail driving tool of the invention, the user can easily see and aim at the point to drive a nail. 
     Moreover, an inner diameter of the eject hole of the contact arm in the vicinity of the forward end of the contact arm in the nail driving direction may be nearly equal to an inner diameter of the injection hole of the driver guide in the vicinity of the forward end of the driver guide in the nail driving direction. 
     In this case, since a nail driven from the injection hole of the driver guide is guided by an inner surface of the eject hole, the nail driven to the outside via the eject hole becomes less easily leaned, thereby a problem like buckling of the nail being prevented. Therefore, driving of a nail can be performed in desirable condition. 
     Moreover, a spike for preventing slippage of the contact arm when driving a nail obliquely may preferably be provided on an outer surface of a forward end portion of the contact arm in the nail driving direction. 
     When a nail is driven obliquely into an object material such as wood and the like, if the spike is stuck in the surface of the object material before driving a nail, the forward end portion of the contact arm can be fixed on the surface and so a nail can be driven exactly at the aimed point. 
     Moreover, there may be further provided with an adapter with a through hole penetrating through the adapter itself along the nail driving direction, which can be detachably attached to the forward end portion of the contact arm in the nail driving direction by inserting the forward end portion into the through hole. At least on one side of the adapter and the forward end portion of the contact arm, a means may be provided for determining a circumferential attachment position which determines a position of the adapter relative to the contact arm among a plurality of different positions along the circumferential direction of the contact arm around a center line of the through hole of the adapter. 
     By using the means, the circumferential attachment position of the adapter can be changed to a desired position without exchanging the adapter to another one, when it becomes necessary to change the circumferential attachment position on driving a nail. 
     Therefore, according to the nail driving tool of the invention, a plurality of adapters corresponding to the respective desired circumferential attachment positions are not necessary and the circumferential attachment position can be changed using only one adapter. 
     Moreover since there is no need to exchange the adapter when changing the circumferential attachment position, the efficiency of the nail driving operation is improved. 
     The means for determining the circumferential attachment position is preferably constituted such that at least two recesses are provided on one side of the inner surface of the through hole of the adapter and the outer surface of the forward end portion of the contact arm, protrusions of one or more, equal to or less than the number of the recesses, are provided on the other side of the surfaces that is not provided with the recesses, and the protrusions are designed to be engaged with the recesses on different positions corresponding to the circumferential attachment position of the adapter relative to the contact arm, when the adapter is attached to the forward end portion of the contact arm. 
     According to the means, the adapter is securely held in the desired circumferential attachment position by engaging the protrusions with the recesses, though the circumferential attachment positions of the adapter are restricted to the positions where the protrusions engage with the recesses. 
     Moreover, a groove is provided on one side of the inner surface of the through hole of the adapter and the outer surface of the forward end portion of the contact arm along the circumference, and on the other side that is not provided with the groove, an engaging protrusion is provided at a position corresponding to the groove. When the adapter is attached to the forward end portion of the contact arm, the engaging protrusion is engaged with the groove. Then, even when the adapter is rotated on the contact arm around the center line of the through hole of the adapter, the engaging protrusion slides in the groove and the position of the adapter relative to the contact arm in the nail driving direction does not change. 
     According to such a nail driving tool, even when the circumferential attachment position of the adapter is changed by the operator&#39;s hand of the nail driving tool after attaching the adapter, the position of the adapter in the nail driving direction can always be kept constant and a driving depth of a nail driven from the nail driving tool in the object can be kept constant. 
     Specifically, if the position of the adapter in the nail driving direction is changed, for example, when the circumferential attachment position of the adapter is changed, the driving depth of the nail driven from the nail driving tool in the object is changed. But by providing the groove and engaging protrusion and engaging them with each other, as mentioned above, the position of the adapter in the nail driving direction can be kept unchanged and driving depth of nails in the object can be always kept constant before and after the circumferential attachment position is changed, even if the circumferential attachment position is changed by the operator&#39;s hand of the nail driving tool after attaching the adapter. 
     If the above-mentioned protrusions and recesses are further provided as well as the above-mentioned groove and engaging protrusion, the protrusions become easily engaged with the recesses when the adapter is rotated around the center line of the through hole of the adapter after attaching the adapter. 
     Specifically, after the adapter is attached, since the position of the adapter in the nail driving direction is always kept constant by the engaging protrusion being slid in the groove during the process of changing the circumferential attachment position, there is no need to do such a work necessary in the case where a groove and an engaging protrusion are not provided, in which a position where the protrusions are properly engaged with the recesses has to be groped for by changing the position of the adapter in the nail driving direction. 
     Moreover, in the above-mentioned nail driving tool, an inner diameter of the through hole of the adapter in the part forward from the position which the edge of the contact arm in the nail driving direction abuts, when the adapter is attached to the forward end portion of the contact arm, may be designed to be equal to or smaller than that of the eject hole of the contact arm in the vicinity of the edge of the contact arm in the nail driving direction. 
     In this case, when the nail-driving operation is carried out, the part of the inner surface of the through hole of the adapter farther than the position which the edge of the contact arm abuts functions as a glide for nails, thereby preventing the nails from leaning while passing along the part or buckling when driven, compared with a nail driving tool wherein the inner diameter of the through hole of an adapter in the part farther than the edge of the contact arm in the nail driving direction is approximately the same as the outer diameter of the contact arm in the vicinity of the edge thereof. 
     Moreover, the adapter may be provided at its end part in the nail driving direction with a projection formed of two opposing outer surfaces of the adapter across the center line of the through hole increasingly approaching a plane including the center line of the through hole of the adapter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a side view of a nail driving tool of the first embodiment; 
     FIGS. 2A and 2B are drawings for explaining a structure of the part around a forward end portion of a contact arm of the first embodiment; FIG. 2A is a longitudinal sectional view of the part; FIG. 2B is a bottom view of the part; 
     FIGS. 3A and 3B are drawings for explaining states of use of the nail driving tool of the first embodiment, using longitudinal sectional views of the part around the forward end portion of the contact arm; 
     FIG. 4 is a drawing for explaining a state of operation carried out with a nail driving tool of the second embodiment; 
     FIGS. 5A and 5B are drawings for explaining a state in which an adapter is attached to a forward end portion of a contact arm of the second embodiment; FIG. 5A is a longitudinal sectional view for explaining a structure of the part of the nail driving tool around the adapter attached; FIG. 5B is a sectional view of FIG. 5A taken along the line B—B′; 
     FIGS. 6A to  6 C are drawings for showing the part around the forward end portion of the contact arm of the nail driving tool of the second embodiment in a state without the adapter; FIGS. 6A,  6 B and  6 C are a side view, a bottom view and a longitudinal sectional view of the part, respectively (FIG. 6C is a longitudinal sectional view of a state in which the adapter is removed from the constituents in FIG. 5A ); 
     FIGS. 7A and 7B are drawings for explaining states of use of the nail driving tool without the adapter of the second embodiment, using longitudinal sectional views of the part around the forward end portion of the contact arm; 
     FIGS. 8A to  8 D are drawings for explaining a shape of the adapter of the nail driving tool of the second embodiment; FIGS. 8A,  8 B and  8 C are a side view, a front view and a bottom view of the adapter, respectively; FIG. 8D is a sectional view of FIG. 8C taken along the line D—D′; and 
     FIG. 9 is a drawing for explaining a state in which an adapter is attached to an forward end portion of a contact arm of a nail driving tool of the third embodiment and is a longitudinal sectional view showing a structure around the part of the nail driving tool where the adapter is attached. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     First Embodiment 
     Referring to FIGS. 1,  2 A, and  2 B, a nail driving tool  1  according to a first embodiment of the present invention is described. 
     The nail driving tool  1  is provided with a main body  2  which houses a driver reciprocally moved by air pressure to drive a nail. A driver guide  3  is connected to the main body  2  so as to extend in the nail driving direction (indicated by an arrow P in FIG. 1) To the side of the driver guide  3  is attached a nail feeding portion  4  for feeding nails into the driver guide  3 . The opposite end of the nail feeding portion  4  to the driver guide  3  is connected to a magazine  5  for housing a rolled assembly of nails (not shown) and feeding the nails into the nail feeding portion  4 . 
     The driver guide  3  includes an injection hole  3   a  (cf. FIG. 2A) through which a nail is driven by the driver. A contact arm  10  having an eject hole  12  (cf. FIGS. 2A and 2B) extending in the nail driving direction is disposed so as to surround the outer surface of a forward end of the driver guide  3  in the nail driving direction. The contact arm  10  is configured to allow slidable movement along an axis  16  along the nail driving direction. The nail driving tool  1  is constituted such that the operation of a trigger  6  for driving a nail is effected by the contact arm  10  being moved in the opposite direction to the nail driving direction. 
     As shown in FIG. 2B, the outer surface  14  of the forward end portion  11  of the contact arm  10  is configured to have an approximately circular cross-section taken along a plane perpendicular to the nail driving direction. 
     The outer surface  14  of the forward end portion  11  is tapered such that the outer diameter thereof is gradually decreased toward an edge  18  in the nail driving direction. Specifically, as shown in FIG. 2A, an inner diameter D1 of the eject hole  12  in the vicinity of the forward end (the edge  13 ) and an inner diameter d1 of the injection hole  3   a  in the vicinity of the forward end of the driver guide  3  are approximately the same. An outer diameter D2 of the contact arm  10  in the vicinity of the edge  13  is equal to or smaller than an outer diameter d2 of the driver guide  3  in the vicinity of the forward end (D2&lt;d2 in the present embodiment). 
     A plurality of spikes  15  (four spikes in the present embodiment) are provided on the outer surface  14  to protrude therefrom. Specifically, the spikes  15  are formed at 90° intervals in the circumferential direction of the outer surface  14  in order to prevent the point to drive a nail from deviating from the right point (i.e. slippage) when driving the nail obliquely into the surface of an object material such as a wooden board. 
     The above-described nail driving tool  1  operates in the following manner. 
     In the case, as shown in FIG. 3A, where a nail  31  is driven obliquely into the surface  30  of the object material, the forward end portion  11  of the contact arm  10  is pressed against the surface  30  so that the spikes  15  are stuck in the surface  30  and the contact arm  10  is retracted backwardly, then a trigger  6  is pulled. As the forward end portion  11  of the contact arm  10  is tapered, it is easy for the user of the nail driving tool  1  to see and aim at the point to drive the nail  31 . Also, as the spikes  15  are stuck in the surface  30 , the forward end portion  11  is fixed on the surface and therefore the user can drive the nail exactly at the aimed point. 
     In the case, as shown in FIG. 3B, where the nail  31  is driven into the surface  30  perpendicularly, the edge  13  is pressed on the surface  30  and the contact arm  10  is retracted backwardly, then a trigger  6  is pulled. Also in this case, as the forward end portion  11  of the contact arm  10  is tapered, it is easy for the user to see and aim at the point to drive the nail  31  A driver  7 , shown in FIGS. 3A and 3B, is reciprocally moved by air pressure along the axis  16  (cf FIG. 1) to drive the nail  31 . 
     In the present embodiment, as explained above, the outer surface  14  of the forward end portion  11  is generally tapered, that is, the outer diameter thereof is gradually decreased toward the edge  13  except some points where the spikes  15  are formed, the user can easily see and aim at the point to drive the nail  31  when driving the nail  31  into the surface  30  from any directions. 
     Also, when the nail  31  is driven obliquely into the surface  30 , the spikes  15  can prevent slippage of the forward end portion  11  on the surface  30 , so that the nail  31  is driven exactly at the aimed point. 
     Moreover, since the inner diameter D1 of the eject hole  12  in the vicinity of the edge  13  and the inner diameter d1 of the injection hole  3   a  in the vicinity of the forward end of the driver guide  3  are approximately the same, the nail  31  injected from the injection hole  3   a  is guided by the inner surface of the eject hole  12  of the contact arm  10  in the vicinity of the edge  13 . As a result, the nail  31  is prevented from leaning while passing along the inner surface or buckling when driven into the surface  30  That is, the nail driving can be performed in desirable condition. 
     Second Embodiment 
     A second embodiment of the present invention is explained with reference to the attached drawings. Similar elements to those in the first embodiment are given the same signs, respectively, and the explanation of the same is omitted or simplified. 
     FIG. 4 shows how to drive nails  31   a ,  31   b  into floorboards  40  as a flooring material to fix the same by using a nail driving tool  100  according to the present embodiment. 
     The floorboard  40  (specifically a floorboard  40   a  other than a floorboard  40   b  with its one side abutting a wall  45 ) has a side protrusion  41  and a side recess  42  on respective sides. The floorboard  40   b  abutting the wall  45  has a side protrusion  41 ′ on the opposite side to the wall  45 . 
     The nails  31   a ,  31   b  are driven into the floorboards  40  obliquely at root corners  41   a ,  41   a ′ of the side protrusions  41 ,  41 ′. Then, the side protrusion  41  is engaged with the side recess  42  of another floorboard  40 , and thus a plurality of floorboards  40  are fixed by repeating the above operation. 
     The nail driving tool  100  according to the present embodiment is provided with an adapter  20  for the floorboard  40  attached on a forward end portion  11  of a contact arm  110  to enable the driving of the nails  31   a ,  31   b . In the nail driving tool  100 , all elements except the adapter  20  and the forward end portion  111  of the contact arm  110  have approximately the same configurations, respectively, as those of the corresponding elements in the nail driving tool  1  of the first embodiment. 
     The adapter  20 , having a through hole  21  extending in a nail driving direction (cf FIGS.  5 A and  5 B), is detachably attached to the forward end portion  111  of the contact arm  110  by engaging the inside of the through hole  21  with the forward end portion  111 . 
     The configuration of the forward end portion  111  of the contact arm  110  is explained in detail with reference to FIGS. 6A through 6C as well as FIGS. 5A and 5B. 
     In the same manner as in the first embodiment, an outer surface  114  of the forward end portion  111  of the contact arm  110  is configured such that it has an approximately circular cross-section taken along a plane perpendicular to the nail driving direction. 
     The outer surface  114  of the forward end portion  111  is also tapered such that the outer diameter thereof is gradually decreased toward an edge  113  in the nail driving direction. Specifically, as shown in FIG. 6C, an inner diameter D1′ of an eject hole  112  in the vicinity of the edge  113  of the contact arm  110  in the nail driving direction and an inner diameter d1′ of an injection hole  3   a  in the vicinity of the forward end of the driver guide  3  are approximately the same. An outer diameter D2′ of the contact arm  110  in the vicinity of the edge  113  (specifically the outer diameter D2′ without taking a later-described spike  115  into account) is equal to or smaller than an outer diameter d2′ of the driver guide  3  in the vicinity of the forward end (D2′ is approximately equal to d2′ in the present embodiment). 
     Therefore, when the nail driving operation is performed without using the adapter  20  as shown in FIGS. 7A and 7B, the user can easily see and aim at a point to drive a nail  31  as in the first embodiment. Also, since the nail  31  injected from the injection hole  3   a  is guided by the inner surface of the eject hole  112  of the contact arm  110  in the vicinity of the edge  113 , the nail  31  is prevented from leaning while passing along the inner surface or being bent when driven into the surface  30 . That is, the nail driving can be performed in desirable condition. 
     An annular protruding spike  115  is formed so as to surround the outer surface  114  of the forward end portion  111  in the vicinity of the edge  113 , which prevents deviation of the nail driving point when driving the nail  31  obliquely into the surface  30 . Specifically by sticking the spike  115  into the surface  30  before the nail driving without using the adapter  20  (cf FIG.  7 A), the forward end portion  111  can be fixed to the surface  30 , so that the user of the nail driving tool  100  can drive the nail  31  exactly at the aimed point. 
     A plurality of recesses  117  (eight recesses in the present embodiment) and a groove  119  are formed in the outer surface  114  of the forward end portion  111  (cf. FIG.  6 A). The eight recesses  117  arranged at 45° intervals in the circumferential direction of the outer surface  114  have approximately the same configuration (cf. FIG.  5 B). The groove  119  is arranged between the recesses  117  of the outer surface  114  and the edge  113  as shown in FIGS. 6A through 6C. The groove  119  formed to extend in the circumferential direction of the outer surface  114  is a perfect annular groove in the present embodiment. 
     The adapter  20  is explained in detail with reference to FIGS. 8A through 8D as well as FIGS. 4,  5 A, and  5 B. 
     The adapter  20  composed of an elastic material such as hard rubber is configured such that the forward end portion  111  of the contact arm  110  is engaged with the through hole  21 . The adapter  20  has a projection  22  or ridge at the end thereof in the nail driving direction. Specifically, at the end of the adapter  20  in the nail driving direction are formed shoulders  22   c ,  22   c ′ in the outer surface  24  of the adapter  20  across the center line  23  (cf. FIG. 8D) of the through hole  21 . The projection  22  includes portions  22   b ,  22   b ′ which are configured such that the outer surface  24  protrudes in the nail driving direction from the ends of the shoulders  22   c ,  22   c ′ on the side of the center line  23  increasingly approaching a plane (not shown) including the center line  23  linearly. In the present invention, an edge  22   a  of the projection  22  in the nail driving direction is on the above plane including the center line  23 . 
     The outer surface  24  of the adapter  20  has a plurality of slits  25  (two slits in the present embodiment) communicating with the through hole  21  and a plurality of elongate protrusions  26  (four protrusions in the present embodiment). 
     The two slits  25  are arranged in the outer surface  24  oppositely across the through hole  21 , that is, at 180° intervals in the circumferential direction of the outer surface  24 . Each of the slits  25  extends from a predetermined point of the outer surface  24  to an upper end  24   a  thereof opposite to the nail driving direction. 
     The four elongate protrusions  26  are arranged at 90° intervals in the circumferential direction of the outer surface  24 , and each of the protrusions  26  extends in the nail driving direction. The four elongate protrusions  26  consists of two longer elongate protrusions  26   a  and two shorter elongate protrusions  26   b . The longer protrusion  26   a  each has an end opposite to the nail driving direction in the vicinity of the upper end  24   a  of the outer surface  24 , and the shorter protrusion  26   b  each has an end opposite to the nail driving direction in the vicinity of a closed end  25   a  of the slit  25 . 
     An inner surface  27  defining the through hole  21  has an approximately circular cross-section taken along a plane perpendicular to the nail driving direction, which is designed to correspond to the configuration of the forward end portion  111 . The inner surface  27  includes an abutting surface  27   a  formed in the nail driving direction, which abuts the edge  113  when the forward end portion  111  is inserted into the through hole  21 . 
     The diameter of the through hole  21  in the part forward from the abutting surface  27   a , which the edge  113  abuts when the adapter  20  is fitted on the forward end portion  111  of the contact arm  110  by engaging the forward end portion  111  with the through hole  21 , is approximately the same as the inner diameter of the eject hole  112  in the vicinity of the edge  113  (cf. FIG.  2 A). As a result, the part functions as a guide for the nail, and therefore prevents the nail from leaning while passing along the part or buckling when driven, compared with a nail driving tool wherein the diameter of the through hole of an adapter in the part forward from the edge of the contact arm in the nail driving direction is approximately the same as the outer diameter of the contact arm in the vicinity of the edge thereof. 
     The inner surface  27  is provided with protrusions  28  of a smaller number (two in the present embodiment) than that of the recesses  117 , and an elongate engaging protrusion  29  (cf. FIGS.  5 B and  8 D). 
     The two protrusions  28  are arranged on the inner surface  27  oppositely across the through hole  21 , that is, at 180° intervals in the circumferential direction of the inner surface  27  and have approximately the same configuration. As described later, the two protrusions  28  are engaged with the corresponding two recesses  117 , respectively, when the adapter  20  is attached on the forward end portion  111  of the contact arm  110 . 
     The engaging protrusion  29  extending along the circumferential direction on the inner surface  27  specifically forms an annular protrusion in the present embodiment. As described later, the engaging protrusion  29  is engaged with the corresponding groove  119  when the adapter  20  is attached on the forward end portion  111  of the contact arm  110 . 
     The adapter  20  is attached to the forward end portion  111  of the contact arm  110 , as shown in FIGS. 4,  5 A and  6 B, in the following manner. 
     Firstly, the forward end portion  111  is inserted into the through hole  21  and the adapter  20  is elastically deformed, whereby the engaging protrusion  29  is engaged with the groove  119  and the edge  113  abuts the abutting surface  27   a.    
     Then, the adapter  20  is rotated around the center line  23  (the axis  16 ) to engage the two protrusions  28  thereof with desired two recesses  117 . The attachment of the adapter  20  is thus completed. 
     Since the adapter  20  in the present embodiment is made of hard rubber, which is relatively easy to elastically deform, and has two slits  25 , even a small force can elastically deform the adapter  20  That is, the user of the nail driving tool  100  can easily attach the adapter  20  with his/her hands. 
     When attaching the adapter  20 , the four elongate protrusions  26  thereof can be used as guides indicating the position of the adapter  20  relative to the forward end portion  111 . 
     The nail driving tool  100  with the adapter  20  attached thereon enables exact nail driving at the root corner  40   a  of the floorboard  40   a . Specifically, as shown in FIG. 4, since the projection  22  of the adapter  20  functions as a guide to properly place the forward end portion  111  of the contact arm  110  at the root corner  41   a , the nail  31   a  is driven exactly at the root corner  41   a  by pressing the edge  22   a  of the projection  22  at the root corner  41   a , thereby retracting the contact arm  110  opposite to the nail driving direction relative to the driver guide  3 , and pulling the trigger  6 . 
     In the nail driving tool  100 , the adapter  20  can be fixed in a circumferential attachment position relative to the contact arm  110  (hereinafter referred to as “a circumferential attachment position”) selected from a plurality of positions along the circumferential direction of the contact arm  110  around the center line  23  (the axis  16 ). Therefore, the nail  31   b  can be driven properly even at the root corner  41   a ′ of the floorboard  40   b  near the wall  45 . If the nail driving tool  100  is used with the adapter  20  in the circumferential attachment position shown in FIG. 4, an end surface  5   a  of the magazine  5  contacts the wall  45  and prevents the nail  31   b  from being driven properly at the root corner  41   a ′ of the floorboard  40   b . However, by changing the circumferential attachment position of the adapter  20  as described below, the nail  31   b  can be driven properly at the root corner  41   a ′ without the end surface  5   a  contacting the wall  45 . 
     The circumferential attachment position of the adapter  20  is changed as follows in the present embodiment. 
     When the adapter  20  is rotated around the center line  23  manually by the user of the nail driving tool  100 , the adapter  20  is deformed such that the two protrusions  28  do not engage with any of the recesses  117  and tops  28   a  of the protrusions  28  facing the center line  23  abut the outer surface  114 . Then, the adapter  20  is further rotated to be in a desired circumferential attachment position where the two protrusions  28  engage with the corresponding two recesses  117 . 
     Since the circumferential attachment position of the adapter  20  can be changed without removing the same as described above, it is not necessary to use a plurality of adapters to obtain the respective desired circumferential attachment. positions. Also, the efficiency of the nail driving operation is improved using the adapter  20  which need not be exchanged. 
     Further, the adapter  20  is securely held in the desired circumferential attachment position even when a big shock of the nail driving is transmitted to the adapter  20 , because the two protrusions  28  are engaged with the two recesses  117  in the circumferential attachment position. 
     The adapter  20  in the desired circumferential attachment position is also securely held in a fixed position in the nail driving direction relative to the contact arm  110  (hereinafter referred to as “a fixed position in the nail driving direction”). Specifically, when the two protrusions  28  are engaged with the two recesses  117 , respectively, with both ends  28   b ,  28   c  thereof along the nail driving direction abutting edges of the recesses  117 , the engaging protrusion  29  is also engaged with the groove  119 , and therefore the adapter  20  is securely held in the fixed position in the nail driving direction. As a result, the nail is driven to the same depth into the floorboard  40  (the object into which the nail is driven) even after the adapter  20  is rotated into another circumferential attachment position. 
     In the present embodiment, once the adapter  20  is attached, the engaging protrusion  29  is always engaged with the groove  119 , which helps the two protrusions  28  engage with another two recesses  117  when the circumferential attachment position of the adapter  20  is changed. In contrast with the case where the groove  119  and the engaging protrusion  29  are not provided, the engaging protrusion  29  slides in the groove  119  when the adapter  20  is rotated, which keeps the adapter  20  in the fixed position in the nail driving direction and saves the labor of groping for the recesses  117  along the nail driving direction. Accordingly, it is relatively easy to engage two protrusions  28  with another two recesses  117 . 
     Both the outer surface  114  of the forward end portion  111  and the inner surface  27  have approximately circular cross-sections in the present embodiment, and therefore the adapter  20  can be rotated smoothly into another circumferential attachment position. 
     Moreover, a click caused at the moment the two protrusions  28  are engaged with the two recesses  117  tells the user of the nail driving tool  100  that the adapter  20  is fixed in position, and thus prevents the nail driving with the adapter  20  out of position. 
     The numbers of the recesses  117  and the protrusions  28 , which are eight and two, respectively, in the second embodiment, are variable when required. Specifically, as long as the protrusions  28  are configured to be engaged with different recesses  117  in accordance with the circumferential attachment position of the adapter  20 , there is no limitation to the numbers of the protrusions  28  and the recesses  117  except that the number of the protrusions  28  is one or more and also equal to or smaller than that of the recesses  117 . 
     The number of the protrusions  28  and the number of the recesses  117  may be the same depending on the configuration of the forward portion of the adapter  20  or for the convenience of the nail driving operation. If eight protrusions  28  corresponding to the eight recesses  117  in the second embodiment are provided, for example, all the eight protrusions  28  are engaged with the eight recesses  117  with the result that the adapter  20  is more securely fixed in the circumferential attachment position. 
     In the case where the adapter  20  is made of a hard material such as metal, the adapter  20  cannot be deformed when attached to the forward end portion  111  as much as in the second embodiment. However, if the recesses  117  are configured as elongate recesses extending to the edge  113  such that the adapter  20  is hardly elastically deformed when engaging the protrusions  28  with the recesses  117 , and the groove  119  and the engaging protrusion  29  are not provided, the adapter  20  can be fixed in one of a plurality of circumferential attachment positions. 
     In this case, to change the circumferential attachment position of the adapter  20 , the adapter  20  is once removed from the forward end portion  111 , rotated to adjust the protrusions  28  thereof to the desired recesses  117 , then attached on the forward end portion  111  again. The adapter  20  is securely fixed in the circumferential attachment position due to engagement of the protrusions  28  and the recesses  117  along with friction between the inner surface  27  and the outer surface  114  of the forward end portion  111 . 
     The groove  119  need not be a continuous annular groove around the outer surface  114  of the forward end portion  111  as in the second embodiment, as long as the engaging protrusion  29  can slides therein when the adapter  20  once attached is rotated into another circumferential attachment position. In the case where the engaging protrusion  29  is an annular protrusion on the inner surface  27  as in the second embodiment, and the outer surface  114  of the forward end portion  111  is configured, at least around the place corresponding to the engaging protrusion  29 , to have an approximately oval cross-section, for example, instead of a circular cross-section, it is necessary to provide the groove(s)  119  extending in the circumferential direction in the outer surface  114  only where the outer diameter of the forward end portion  111  is relatively large. 
     The engaging protrusion  29 ′ need not be a continuous annular protrusion on the inner surface  27  as in the second embodiment, as long as the engaging protrusion  29  can slides in the groove  119  when the adapter  20  once attached is rotated into another circumferential attachment position. In the case where the groove  119  is a continuous annular groove as in the second embodiment, it is necessary to provide the engaging protrusions  29  only at the place corresponding to the groove  119  on the inner surface  27 . 
     Oppositely to the second embodiment, the recesses  117  may be provided in the inner surface  27 , and the protrusions  28  on the outer surface  114  of the forward end portion  111 . Also, the groove  119  may be provided in the inner surface  27 , and the engaging protrusion  29  on the outer surface  114  of the forward end portion  111 . 
     Furthermore, instead of providing the above described recesses  117 , the protrusions  28 , the groove  119 , and the engaging protrusion  29 , the adapter  20  may be designed to be fixed on the forward end portion  111  merely due to friction between the inner surface  27  and the outer surface  114  of the forward end portion  111 . Specifically, the adapter  20  composed of an elastic material such as rubber or plastic is deformed, when attached on the forward end portion  111 , in accordance with the configuration thereof and fixed thereon due to friction between the inner surface  27  and the outer surface  114  of the forward end portion  111 . In this case, even when the adapter  20  once attached is rotated into another desired circumferential attachment position by the user of the nail driving tool  100 , the adapter  20  is deformed in accordance with the configuration of the forward end portion  111  and fixed in the circumferential attachment position due to the above mentioned friction. This type of adapter  20  enables its fixation in any desired circumferential attachment position on the forward end portion  111  even during the nail driving operation, therefore the efficiency of the operation is improved. 
     The edge  22   a  of the projection  22  of the adapter  20  in the nail driving direction, which is on a plane including the center line  23  of the through hole  21  in the second embodiment, may be configured to be off the above plane when required. 
     The portions  22   b ,  22   b ′ of the projection  22 , which are configured to protrude in the nail driving direction increasingly approaching a plane including the center line  23  linearly in the second embodiment, may be configured to approach the above plane curvedly when required. 
     The inner diameter D1′ of the eject hole  112  in the vicinity of the edge  113  and the inner diameter d1′ of the injection hole  3   a  near the forward end of the driver guide  3  in the nail driving direction, which are approximately the same in the second embodiment, may be such that D1′&gt;d1′. In this case, the diameter of the through hole  21  of the adapter  20  is preferably smaller than D1′, forward in the nail driving direction from the abutting surface  27   a  (i.e. the place at which the edge  113  of the contact arm  110  is located). In the second embodiment, since D1′ and d1′ are approximately the same, the inner surface  27 , whose inner diameter is equal to D1′ forward in the nail driving direction from the abutting surface  27   a , can function as a nail guide. However, when D1′&gt;d1′, the inner diameter of the through hole  21  forward in the nail driving direction from the abutting surface  27   a  is preferably smaller than D1′ so as to make the inner surface  27  function effectively as the nail guide. Further preferably, in this case, the inner diameter forward in the nail driving direction from the abutting surface  27   a  is approximately equal to D1′ at least at a point in the vicinity of the edge  113  of the contact arm  110  and tapers in the nail driving direction so that the nail can pass the point without having its tip stuck. 
     Third Embodiment 
     Referring to FIG. 9, a third embodiment of the present invention is described. Similar elements, to those in the second embodiment are given the same signs, respectively, and the explanation of the same is omitted or simplified. 
     A nail driving tool according to the present embodiment is provided with an adapter  20 ′ for the floorboard  40  attached on the forward end portion  111  of the contact arm  110  as the nail driving tool  100  of the second embodiment. 
     The only difference is that the adapter  20 ′ does not have the shoulders  22   c ,  22   c ′ included in the adapter  20 . Specifically, the adapter  20 ′ has a projection  51  configured such that portions  51   b ,  51   b ′ of the outer surface  24  across the center line  23  increasingly approach a plane (not shown) including the center line  23  linearly. 
     Compared with the adapter  20  of the second embodiment, the adapter  20 ′ enables the user to see more easily the edge  51   a  of the projection  51  (i.e. the point to drive a nail) which is placed at the root corners  41   a ,  41   a ′ of the floorboards  40  when driving the nails  31   a ,  31   b  thereat. Accordingly, by using the nail driving tool of the present embodiment, the nails  31   a ,  31   b  are driven further precisely at the root corners  41   a ,  41   a ′ as well as similar operation to that of the second embodiment can be achieved. 
     It is to be understood that the present invention is not limited to the embodiments described above, but may be embodied in various forms without departing from the spirit of the invention. 
     For example, although the adapter  20  ( 20 ′) for the floorboard  40  is attached on the forward end portion  111  of the contact arm  110  to drive the nail exactly at the root corners  41   a ,  41   a ′ of the floorboards  40  in the second and third embodiments, the edge  13  ( 113 ) of the forward end portion  11  ( 111 ) can be easily placed close to the root corners  41   a ,  41   a ′ without using the adapter  20  ( 20 ′) because the outer diameter of the outer surface  14  ( 114 ) in the forward end portion  11  ( 111 ) of the contact arm  10  ( 110 ) is tapered in all the three embodiments. As a result, the nails can be driven relatively precisely at the root corners  41   a ,  41   a ′ without the adapter  20  ( 20 ′). 
     When driving the nails at the root corners  41   a ,  41   a ′ without using the adapter  20  ( 20 ′), the outer surface  14  ( 114 ) of the forward end portion  11  ( 111 ) is preferably chamfered in accordance with the shape of the floorboard  40  around the root corners  41   a ,  41   a ′. 
     While the outer diameter of the outer surface  14  ( 114 ) in the forward end portion  11  ( 111 ) of the contact arm  10  ( 110 ) is tapered in all the three embodiments, a cylindrical portion having a fixed diameter may be provided to extend from the tapered end in the nail driving direction.