Length adjustment mechanism

Claim 1

IN LENGTH ADJUSTMENT MECHANISM FOR A DEVICE HAVING ELONGATE OVERLAPPING PARTS FORMED AS RESPECTIVE GEAR RACKS DISPOSED IN MUTUALLY SPACED, CONFRONTING RELATIONSHIP, SAID MECHANISM COMPRISING A CASING FOR RECEIVING AND HOUSING SAID OVERLAPPING PARTS, SAID CASING BEING OF OPEN-ENDED TUBULAR FORMATION AND HAVING AN APERTURE OPENING INTO ITS INTERIOR FROM THHE ETERIOR THEREOF INTERMEDIATE ITS LENGTH; A RING GEAR ENCIRCLING THE APERTURE AND RIGIDLY SECURED TO THE CASING; A PINION WITHIN THE CASING IN MESH WITH BOTH SAID GEAR RACKS AND HAVING A SHAFT EXTENDING RIGIDLY THEREFROM TOWARD THE APERTURE AND CONCENTRIC WITH THE RING GEAR; A KNOB AND SPUR GEAR ASSEMBLY MOUNTED CONCENTRICALLY ON AND ENGAGING THE SHAFT FOR ROTATING IT AND THE PINION, THE KNOB OF SAID ASSEMBLY BEING DISPOSED EXTERNALLY OF THE CASING AT THE APERTURE; RESILIENT MEANS NORMALLY URGING SAID ASSEMBLY SO THAT THE SPUR GEAR IS BROUGHT INTO INTERMESHING ENGAGEMENT WITH THE RING GEAR TO LOCK SAID KNOB, SPUR GEAR, SHAFT, AND PINION AGAINST ROTATION; AND MEANS RETAINING SAID ASSEMBLY ON THE SHAFT, SAID ASSEMBLY BEING SLIDABLE AXIALLY ALONG THE SHAFT AGAINST THE URGE OF THE RESILIENT MEANS FOR DISENGAGING THE SPUR GEAR FROM THE RING GEAR AND PERMITTING ROTATION OF SAID KNOB, SPUR GEAR, SHAFT, AND PINION FOR LENGTH ADJUSTMENT PURPOSES, THE IMPROVEMENT COMPRISING CAMMING MEANS ARRANGED BETWEEN AND COUPLING SAID KNOB AND SAID SPUR GEAR, SO THAT ROTATION OF THE KNOB WILL CAM THE SPUR GEAR AGAINST THE URGE OF SAID RESILIENT MEANS AND SLIDE IT AXIALLY OUT OF LOCKING ENGAGEMENT WITH THE RING GEAR.