turning now to the drawings , in which similar reference characters denote similar elements throughout the several views , fig1 , 4 and 6 illustrate an automatic screw gun 10 comprising a housing 12 having an exit port 14 , best seen at the lower left of fig4 and a handle 16 . handle 16 is constrained by a guide assembly 18 to move in a short path along housing 12 when depressed for operation , as will be described further hereinafter . fig1 illustrates the invention with the handle 16 in the normal position . fig7 shows the handle fully depressed . enclosed within housing 12 , and as best seen in fig4 a driver shaft 20 has a tip 22 on a lower end 24 . the driver shaft 20 is suitably journaled within the housing 12 . a coupling structure 26 carries an upper end 28 of the driver shaft 20 in a rotatable manner and at a right angle to the handle 16 , so that the driver shaft 20 will move in tandem with the handle 16 towards the exit port 14 when the handle 16 is depressed . coupling structure 26 includes a thrust bearing ( not separately shown ) to enable driver shaft to rotate while being depressed simultaneously with handle 16 . driver shaft 20 is connected to a motor 80 by a drive train 30 contained within housing 12 . drive train 30 will be further described hereinafter . a plurality of screws 32 , shown illustratively isolated from screw gun 10 in fig2 are each provided with a head 34 and threaded shank 36 . the heads 34 are attached to each other in a row by a bead or stratum of lacquer , adhesive or frangible tape ( none of these shown ) applied to the top of the heads 34 . a magazine 38 holds the screws 32 within the housing 12 parallel to and spaced away from the handle 16 . the head 34 of the forward screw 32 is directly under the tip 22 of the driver shaft 20 and the threaded shank 36 is above the exit port 14 . driver shaft 20 is directed towards exit port 14 , so that screws are dispensed through port 14 . when the user operates screw gun 10 , the tip 22 of the driver shaft 20 engages the head 34 of the forwardmost screw 32 , that is , the screw positioned directly below driver shaft 20 . depression of handle 16 and of driver shaft 20 will then engage and rotate the forwardmost screw 32 . this screw 32 is then dispensed through exit port 14 and threads into the work piece 42 . the housing 12 is in a generally u - shaped configuration having a flat , hollow base 44 and two extending , spaced apart hollow arms 46 and 48 . the exit port 14 is located at one end of the hollow base 44 under the first hollow arm 46 . the handle 16 includes a plurality of finger grips 50 and a trigger 52 operating a switch to energize the motor 80 . the guide assembly 18 comprises a pair of open passageways defined within the walls of housing 12 . each passageway encloses one of two ends 74 of handle 16 , so that handle 16 is constrained to travel towards and away from base 44 in a path limited by the extent of these passageways . a return mechanism biasing handle 16 to return to the retracted position illustrated in fig1 and 4 comprises two substantially identical return assemblies also housed within arms 46 and 48 . each return assembly includes a compression spring 56 which acts on one end 74 of handle 16 . each return assembly also incorporates a shock absorber 58 for damping excessively abrupt return of handle 16 to its original position , as might occur if handle 16 were suddenly released . shock absorber 58 comprises a plunger 59 contained within a cylindrical housing , as best seen in fig5 . the plunger 59 is driven by a stem 61 anchored at an end 74 of handle 16 . the floor 63 of this cylinder supports a relief valve 65 enabling air to escape when compressed by the plunger 59 . a spring 67 incorporated into the valve 65 also slows rapid descent of the plunger 59 and hence also slows descent of handle 16 . resistive force exerted by the spring 67 is sensed by the user , and serves notice that handle 16 is approaching the lower limit of its permissible travel . turning now to fig6 the driver shaft 20 includes a lower end 24 having a square shaped bore 60 formed therein with a side slot 62 affording access into the bore 60 . the tip 22 is a separate magnetic replaceable bit 64 , having a square shaped shank 66 that is insertable into the bore 60 . the bit 64 may be removed from the bore 60 by prying . to do this , a small bladed tool ( not shown ) is inserted through the slot 62 . a square shaped magnet 68 is placed within the bore 60 , behind the bit 64 , to hold the head 34 of an engaged screw 32 against the bit 64 . of course , once driven into the work piece 40 , the screw 32 will no longer be retained by magnetic attraction . with particular reference to fig4 the coupling structure 26 entraps the tapered portion 70 of the upper end 28 of the driver shaft 20 between a pair of ball bearing assemblies 72 . ball bearing assemblies 72 are carried on one end 74 of handle 16 . raising and lowering of handle 16 therefore also raises and lowers driver shaft 20 , since the upper end 28 of the driver shaft 20 is entrapped between ball bearing assemblies 72 . drive train 30 will now be discussed . driver shaft 20 has splines 76 extending along the entire length thereof , below upper end 28 . splines 76 enable geared engagement of driver shaft 20 with a spur gear 78 . spur gear 78 is supported by suitably journaling a first shaft 82 at a fixed point within housing 12 . a second or output shaft 84 extends from the motor 80 . shafts 82 and 84 are connected by a third shaft 86 . shaft 86 is suitably journaled within housing 12 proximate the hollow base 44 . a first set of intersecting bevel gears 88 rotatably connects the first shaft 82 with the second shaft 84 . a second set of intersecting bevel gears 90 connects the third shaft 86 and the second shaft 84 , so that rotation of the motor 80 will be transferred to the spur gear 78 , to rotate the driver shaft 20 . it will be appreciated that due to the length of the splines 76 , driver shaft 20 will be rotated even when it is moved vertically upwardly and downwardly as handle 16 is depressed and released . magazine 38 comprises three plates 92 secured in position by attachment to the hollow base 44 under the first hollow arm 46 . the three plates 92 are disposed on three sides of the forwardmost screw 32 . the fourth side is occupied by the row of screws in storage , as will be explained further hereinafter . one plate 92 is clearly visible in fig4 two surrounding plates 92 being removed for clarity in this view . these two surrounding plates 92 are seen in fig3 . plates 92 hold the forward screw 32 in an upright position for engagement by tip 22 of driver shaft 20 . plates 92 are slightly flexible , being constructed of spring steel or a similar material , so that they spread or deflect to allow passage of a screw 32 when being driven by driver shaft 20 . plates 92 return to their normal position by resilience of the constituent material . a magazine pressure block 94 bears against the head 34 of the rearward screw 32 , thereby urging the row of screws 32 towards a forward position beneath driver shaft 20 . a partially surrounding trough serving as a channel 96 is mounted longitudinally within the hollow base 44 , directly under and parallel to the third shaft 86 . channel 96 comprises a major component of magazine 38 , holds a supply of screws 32 , and opens to an opposite side of the hollow base 44 , under the second hollow arm 48 . channel 96 is v - shaped when viewed from the end , so as to cooperate with the generally conical heads 34 of screws 32 . channel 96 is open at the bottom to enable shanks 36 of screws 32 to pass therethrough . channel 96 provides sufficient clearance to hold screws 32 in a generally vertical orientation as depicted in fig4 and 6 , and loosely enough to allow screws 32 to slide towards the forward position responsive to spring pressure . an access door 98 closes channel 96 , providing access to channel 96 enabling the supply of screws 32 to be renewed when depleted . an elongated spring 100 within the channel 96 is connected at its proximal end to the magazine pressure block 94 , while the distal end of the spring 100 bears against the door 98 when door 98 is closed . this arrangement assures that the magazine pressure block 94 will always bear against the head 34 of the rearward screw 32 . in turn , this pressure acts to propel the entire row of screws 32 so that there is always one screw 32 in the forward position beneath driver shaft 20 . a marker line or indicia 102 on a side of the hollow base 44 indicates alignment of the forward screw 32 with respect to the work piece 42 . a window 104 on the side of the hollow base 44 reveals remaining supply of screws 32 present within channel 96 . a slidably removable panel 106 located on the side of the hollow base 44 directly next to the lower end 24 of the driver shaft 20 affords access to slot 62 ( see fig6 ), so that the bit 64 can be removed and replaced when needed . the depressed position of handle 16 is shown in fig7 . it will be seen that handle 16 has members cooperating with arms 46 and 48 to enable travel between the positions shown in fig1 and fig7 and indicated by an arrow in fig7 . at one end 74 , that being the end towards the top of fig7 handle 16 is configured to cooperate with the open space or cavity defined within the walls of arm 46 . at the lower end , as depicted in fig7 handle 16 has fingers 17 which ride within cooperating slots 54 . handle 16 thus cooperates with housing 12 at both ends of handle 16 , thereby avoiding binding as handle 16 is raised and lowered relative to the surface of the work piece 42 ( see fig1 ). the first hollow arm 46 has a side slot 108 therein , approximately half way down from the handle 16 . a slide bolt 110 mounted on the end 74 of the handle 16 can penetrate slot 108 when the handle 16 is fully depressed . this creates an interference , thereby locking handle 16 in the fully depressed position . slide bolt 110 is clearly seen in fig1 to include a projection affording engagement by the user &# 39 ; s finger . fig7 shows one end of slide bolt 110 projecting through slot 108 after handle 16 has been fully depressed . fig4 shows a reverse and forward switch 112 mounted on the end 74 of the handle 16 next to the slide bolt 110 . the switch 112 is electrically connected to the motor 80 by a flexible electrical cable ( not shown ), so that the operator has full access to switch 112 regardless of whether handle 16 has been depressed . the switch 112 is a reversing switch for enabling the motor 80 to thread screws 32 into the work piece 40 and also to withdraw screws if desired . it will be understood that each of the elements described above , or two or more together may also find a useful application in other types of methods differing from the type described above . while certain novel features of this invention have been shown and described and are pointed out in the appended claims , the invention is not intended to be limited to the embodiment set forth above , since it will be understood that various omissions , modifications , substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention . without further analysis , the foregoing will so fully reveal the gist of the present invention that others can , by applying current knowledge , readily adapt it for various applications without omitting features that , from the standpoint of prior art , fairly constitute essential characteristics of the generic or specific aspects of this invention .