diameter of the bore hole in which the tool is received thus if the tool 10 is to be utilized in a different bore hole an outboard portion 15 of different length appropriate to the bore hole diameter will be utilized the inboard portion 17 of arm 12 is slotted so as to fit over a rotator 18 disposed within a recess 20 provided within the tool 10 the contours of the rotator 18 are best shown in fig4 and 5 the rotator is attached by a pivot pin 21 to a slideable actuator block 22 a second pivot pin 23 connects the rotator 18 to a rotating link 24 which is in turn attached by a third pivot pin 25 to a fixed portion of the tool 10 this arrangement provides for rotation of the rotator 18 when the actuator block 22 is moved relative to the body of the tool 10 such movement is effected by an actuator rod 26 connected to block 22 movement of the actuator rod in response to signals sent from the surface may be effected by any conventional means in the embodiment shown in fig1 a motor driven nut 27 motor not shown engages threads 28 on rod 26 to advance or retract the actuator block 22 an actuator rod extension 30 projects from the upper end of the block 22 and serves two functions first both the actuator rod 26 and the extension 30.