referring now to fig1 a pneumatic ground piercing tool 10 according to the invention includes , as main components , a tool body 11 , a striker 12 for impacting against the interior of body 11 to drive the tool forward , a stepped air inlet conduit 13 which cooperates with striker 12 for supplying compressed air to reciprocate striker 12 , and a tail assembly 14 which allows exhaust air to escape from the tool , secures conduit 13 to body 11 , and provides a threaded connection to allow reverse operation . each of these components will now be described in detail . tool body 11 comprises a cylindrical hollow housing 21 having a tapered nose 22 . nose 22 can be made by swaging a front end portion of a tubular steel pipe against a frontwardly tapering , generally frustonconical forming anvil . after swaging is completed , the forming anvil is removed , and the swaged housing is reheated . the anvil 23 is then inserted into the housing as shown in fig1 . anvil 23 is nearly identical in shape to the forming anvil , except that it has a cylindrical front end portion 25 which has a slightly greater diameter than the corresponding portion of the forming anvil , and a rear end portion 29 has a slightly smaller diameter than the corresponding portion of the forming anvil . this assures that anvil 23 will remain securely coupled to housing 21 during use of the tool . the rear end of the pipe is then cut to size , and the interior of housing 21 is then machined to provided a counterbore 24 of slightly enlarged inner diameter . screw threads 26 are then cut on the interior surface of housing 21 inwardly of but near to counterbore 24 to allow the tail assembly to be secured thereto , as described hereafter . the foregoing method of forming body 11 according to the invention , utilizing generally known swaging techniques , substantially reduces the amount of material ( steel ) needed to make tool 10 . striker 12 is disposed for sliding , back - and - forth movement inside of tool body 11 forwardly of conduit 13 and tail assembly 14 . striker 12 comprises a cylindrical rod 31 having frontwardly and rearwardly opening blind holes ( recesses ) 32 , 33 respectively therein . a pair of plastic , front and rear seal bearing rings 34 , 36 are disposed in corresponding annular grooves 37 , 38 in the outer periphery of rod 31 for supporting striker 12 for movement along the inner surface of body 11 . annular front impact surface 39 impacts against anvil 23 when the tool is in forward mode , as shown in fig1 and an annular rear impact surface 41 impacts against tail assembly 14 when the tool is in rearward mode . a plurality of rear radial holes 42 allow communication between recess 33 and the annular space 43 between striker 12 and body 11 bounded by seal rings 34 , 36 . a second set of front radial holes 44 allow communication between space 43 and front recess 32 . annular space 43 , holes 44 , front recess 32 and the interior space of body 11 ahead of striker 12 ( after striker 12 has moved backwards from the position shown in fig1 ) together comprise the front , variable pressure chamber of the tool . anvil 23 may optionally have a narrow central air passage ( not shown ) allowing limited communication between the front pressure chamber and the front end of the tool for injecting air into the hole being formed to loosen the soil ahead of the tool . referring now to fig1 through 5 , stepped air inlet conduit 13 includes a flexible hose 51 , a tubular bushing 52 fitted with an inner locking nut 53 , and an adjuster screw mechanism 54 . hose 51 , which may be made of rubberized fabric , is secured by a coupling ( not shown ) to a further length of hose which ultimately connects tool 10 with the air compressor . the inner end of hose 51 is clamped to the inner wall of bushing 52 by nut 53 , which is threadedly coupled with bushing 52 . nut 53 has a bore 56 which allows compressed air to pass from hose 51 through nut 53 and bushing 52 into cavity 33 . in the alternative , hose 51 may be adhesively bonded directly to the interior of bushing 52 , and nut 53 may be omitted . the cylindrical outer surface of bushing 52 is inserted into cavity 33 in slidable , sealing engagement with the wall thereof . cavity 33 and the adjoining interior space of stepped conduit 13 together comprise a rear , constant pressure chamber which communicates intermittently with the front , variable pressure chamber by means of holes 42 . bushing 52 may , if needed , have a plastic bearing ring 57 disposed in an annular peripheral groove 58 to reduce air leakage between bushing 52 and the wall of cavity 33 . adjuster screw mechanism 54 includes a tubular inner sleeve 61 disposed inside of hose 51 and a coaxial outer sleeve 62 which has outer peripheral threads 63 for securing the stepped conduit 13 to tail assembly 14 , as described below . hose 51 is clamped under compression between sleeves 61 , 62 as shown in fig5 and 6 . outer sleeve 62 may , in addition , be secured to the outside of hose 51 by an adhesive . if the adhesive bond is sufficiently strong , inner sleeve 61 may be omitted . the foregoing structure renders mechanism 54 light in weight , which reduces the effect of axial shocks transmitted thereto through sleeve 62 and helps eliminate the need for a shock dampening coupling . for this purpose , bushing 52 is preferably made of a light - weight material such as aluminum , and outer sleeve 62 is made as short as possible , e . g . only about half or less the length of the threaded hole in which it is mounted . sleeve 62 preferably is only long enough to provide enough screw thread turns to effect the operating mode change , i . e ., about 6 or less . tail assembly 14 includes a tail nut ( rear anvil ) 71 and a end cap ( cone ) 72 secured together by bolts 73 . tail nut 71 has outer peripheral threads 74 in engagement with threads 26 on the interior of housing 21 , and an end flange 76 for retaining nut 71 in counterbore 24 . nut 71 further has a central hole 77 having screw threads 78 in engagement with threads 63 of sleeve 62 . threads 78 have blind front ends so that movement of sleeve 62 is limited to the forwardmost position shown in fig1 . threads 78 open rearwardly so that air inlet conduit 13 can be unscrewed and removed from nut 71 . an inner end boss 75 of cap 72 limits rearward movement of sleeve 62 to a rearwardmost position when cap 72 is secured to nut 71 so that sleeve 62 cannot become disengaged from nut 71 during operation . according to a preferred embodiment of the invention , threads 63 , 78 are formed in a double helix having a helix angle in the range of about 7 to 10 degrees , particularly 8 to 9 . 5 degrees . the double helix threading provides the connection with additional strength , while allowing a large axial displacement for each turn of hose 51 . the large helix angle reduces the tendency of the threaded coupling to become locked , but is not so large that the adjuster screw mechanism will unscrew too easily . threads 63 , 78 preferably have a height and width of at least about 0 . 1 inch , especially 0 . 1 to 0 . 25 inch , to provide a stronger coupling better able to withstand shocks transmitted through nut 71 from the tool body . tail nut 71 is provided with a plurality of exhaust passages 79 and blind threaded holes 81 for receiving bolts 73 . passages 79 and holes 81 are parallel to each other and to central hole 77 , and are most advantageously arranged in a circular formation as shown in fig2 and 3 . since the power of the tool increases as the cross - sectional area of the exhaust passages increases , this construction allows tool power to be maximized without weakening nut 71 excessively . prior tools employing large resilient shock absorbers having exhaust passages formed therein are more limited in the area available for forming exhaust passages . the present invention , by eliminating the need for a large resilient shock absorber to protect the screw reverse connection from shocks , provides a more powerful tool . tail cap 72 has a series of exhaust openings 82 preferably of the same dimensions as exhaust passages 79 . openings 82 prevent stones from becoming jammed between the tail assembly and the hose coupling , referred to above , which is behind the tool instead of inside the tailpiece as in prior tools . cap 72 also has a large central hole 83 through which hose 51 passes , and a rearwardly tapering outer surface 84 to facilitate reverse movement . the foregoing tail assembly further enhances the serviceability of the tool . the large , unitary tail pieces used in prior tools must be tightly secured in the rear end of the tool body in order to ensure that the tail piece will remain in place during use . the torque required to unscrew the tailpiece is great , making the tool very difficult to take apart . by contrast , bolts 73 can provide the needed clamp load to lock the tail assembly in position , but require far less torque to unscrew . once bolts 73 have been loosened , nut 71 , cap 72 and bolts 73 can be easily turned in unison to remove the tail assembly . referring now to fig6 an alternative embodiment of a striker 12a according to the invention is filled with a vibration dampening material , such as steel shot 91 . shot 91 is confined in a annular chamber 92 between chambers 32 , 33 by a pair of front and rear plugs 93 , 94 through which a double - ended bolt 96 is inserted . a pair of nuts 97 , 98 mounted on opposite threaded ends of bolt 96 hold plugs 93 , 94 in position . shot 91 dampens vibrations which arise as striker 12a impacts against the associated anvil , greatly reducing the amount of noise made by the tool during operation . fig7 and 9 illustrate alternative constructions for the stepped conduit 13 . in fig7 hose 51 is broken into sections 51a and 51b . outer sleeve 62 is in direct contact with an enlarged diameter central portion of a modified inner sleeve 61a . a pair of front and rear plastic couplings 101 , 102 isolate sleeve 62 from hose sections 51a , 51b . couplings 101 , 102 may be made of high density polyurethane . sleeve 62 is slightly separated from couplings 101 , 102 , and may slide along the outer surface of sleeve 61a into either of couplings 101 , 102 , which act as shock absorbers . a pair of clamps 103 , 104 secure hose sections 51a , 51b to inner sleeve 61a and couplings 101 , 102 , respectively . in fig8 clamps 103 , 104 are used to further secure the screw adjuster mechanism , and couplings 101 , 102 are omitted . in fig9 an elastomeric shear coupling 106 is interposed between inner and outer sleeves 61a , 62 to provide additional shock dampening effects . shear coupling 106 is adhesively bonded to sleeves 61a , 62 . it will be understood that the foregoing description is of preferred exemplary embodiments of this invention , and that the invention is not limited to the specific forms shown . for example , the described mechanism for providing a flexible hose with a threaded outer sleeve could be used in other applications wherein it is desired to threadedly secure a hose to a fixture . these and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims .