out of the well for routine maintenance and cleaning the operators can easily determine if the wall partition 7 has been compromised by moving the utility sub 1 of the present invention and listening for the steel ball 20 to rattle around if the wall partition 7 has been compromised and the cavity 6 contains any drilling fluids the steel ball 20 will be restricted in its movement within the cavity 6 now referring to fig5 it will be seen that a conventional drill bit 20 e g a three cone rock bit is mounted at the bottom of a string of pipe immediately above the bit 20 is the sub assembly 1 of the present invention the outer surface of the sub assembly 1 is preferably but not necessarily concentric with or symmetrical with respect to its longitudinal axis one side of the sub assembly 1 is however heavier than the other so that as the drill string rotates the sub assembly 1 will tend to revolve or gyrate about the longitudinal axis of the string it is however neither necessary nor desirable for the sub assembly 1 itself to swing far enough out of line to brush against the wall of the well as the.