assembly 11 with the shells temporarily split apart however it would also be possible to use a single tube for the housing 38 by employing a different method of assembly thus the invention herein contemplates that both the shell and the single tube constructions are structurally and functionally equivalent and that one of ordinary skill in the art may have design justifications to substitute one for the other each shell includes an upper cam follower 44 and a lower cam follower 46 each cam follower 44 and 46 is bent slightly inwardly toward inner sleeve 32 in this manner the upper cam followers 44 engage respective upper cam surfaces 33 of the inner sleeve 32 similarly the lower cam followers 46 engage respective lower cam surfaces 34 each shell further includes an elongated tooth slot 47 in its sidewall portion each tooth slot has a tooth rack 48 extending along one side the tooth slots 47 have a transverse dimension which is sufficient to accommodate sliding of the locking teeth of tooth plate 21 when the tooth plate is rotated into a disengaged unlocked position a tubular outer sleeve 49 is provided around the housing 38 sleeve 49 has an inner diameter which is just slightly larger than the outer diameter of housing 38 on opposing sidewalls of its lower end the outer sleeve 49 has longitudinally extending sidewall recesses 51 shells 39 and 41 include locking fingers 52 extending slightly outwardly.