Abstract: An apparatus for engagement of cylindrical members about the outside diameter, so that downhole tools may be positioned longitudinally along said cylindrical member. A generally cylindrical outer ring is detachably engaged with a generally cylindrical inner ring. Once the inner ring is detached from the outer ring it is automatically present into position by a spring clamping force exerted between the pipe and inner ring. Relative axial motion of the outer ring with respect to the inner ring automatically energizes the inner ring inward providing the high clamping force required to set the self energizing stop collar in its final position.