101 has a slot 109 through which a screw 111 extends screw 111 is tightened to securely fix cylinder 107 in support 101 to give the assembly an overall 34 t 34 shape as can be seen in fig1 sight 81 has a cylindrical platform 113 from which an arm 115 extends arm 115 has a smaller diameter than base 113 and forms a shoulder 117 on base 113 a pair of pins 119 extend from shoulder 117 on opposite sides thereof a screw 121 extends from arm 115 as seen in fig3 arm 115 is received in a central bore 123 of cylinder 107 and pins 119 are received in blind bores 125 the cooperation of pins 119 and bores 125 prevent rotation of sight 81 with respect to cylinder 107 cylinder 107 has a front end 127 which defines a smaller bore 129 through which screw 121 extends surface 127 also has a plurality of semi circular depressions or sockets 131 formed in a circular pattern fig2 a knob 133 having a knurled top 135 and a threaded bore 137 is received on screw 121 by rotating knob 133 sight 81 can be moved toward or away from cylinder 107 a spring 139 is received in bore 123 between end 127 and a shoulder 141 on arm 115 spring 139 biases sight 81 outwardly.