cable coupling a cylindrical cavity 17 or bore extends the entire length of the housing 11 this cavity 17 is concentric with the longitudinal center line of the housing 11 and extends entirely therethrough from the coupling end 13 on to which it opens to be circumferentially traversed by the tapered shoulder 15 an annular shoulder 19 projects within the cylindrical cavity 17 at about mid length although the precise position of this shoulder 19 is not critical this shoulder 19 provides opposed abutment faces on either side thereof which are normal to the center line of the cavity 17 the annular shoulder 19 is essentially a ring which is approximately 1 16 inch to 1 8 inch thick the cavity 17 has a 17 32 inch inside diameter on the coupling 13 side of the shoulder 19 and a 1 2 inch on the other alternately the cavity 17 can have a uniform diameter throughout its length the opposite end of the housing 11 from the coupling end 13 is the driving end 21 which is threaded a distance of about 1 2 inch with american standard thread at approximately 20 threads per inch a threaded cap 23 mates with the driving end threads 21 and screws down to seal off the cavity 17 which opens onto that end 21 a hole 25 is drilled and tapped through the wall of the cylindrical housing 11 at the coupling end 13 side of the annular shoulder 19 this hole 25 is fitted with a.