for receipt in the chuck 14 of the drill 10 and an actuator thread 66 of left hand thread for threaded engagement with the threaded counterbore 54 of the nosepiece 24 the fastener section 62 includes a center section 68 having a clearance relation with the threaded counterbore 54 and terminating with a threaded end 70 of right hand thread for threaded engagement with tile fastener 30 accordingly upon relative rotation of the nosepiece 24 and the shaft 26 the threaded end 70 is shifted between an extended position shown in fig1 and a retracted position shown in fig1 referring to fig3 and 4 the yoke 20 comprises a support sleeve 80 a pair of mounting arms 82 and a mounting clamp 84 the support sleeve 80 includes a through bore 86 of a hexagonal cross section for axially telescopically supporting the head section 50 of the nosepiece 24 and a cylindrical outer surface 88 each of the arms 82 has a generally rectangular cross section and includes a front section 90 fixedly connected to the sleeve 80 at welds 92 an outwardly flared center section 94 and a rearwardly extending rear section 96 connected to the outer surface of the mounting clamp 84 the mounting clamp 84 includes a split cylindrical adjustable band 100 telescopically receivable over the frontal nose of the drill housing 22 and a pair of circumferentially spaced radially outwardly turned legs 102 adjustably interconnected by bolt and nut fastener assembly 104 as will be apparent the band 100 may be adjustably fixedly.