AN IMPROVED SUB ASSEMBLY

摘要

A sub assembly for coupling to a drill string, the assembly comprising; a mandrel; a sleeve arranged to be co-axially positioned about said mandrel; a first stop arranged to prevent axial movement of the sleeve along the mandrel in a first direction; a second stop arranged to prevent axial movement of the sleeve in a second direction; wherein said second stop is releasably engageable from the mandrel.