Height adjustment mechanism suitable for a footring

A footring adjustment mechanism comprising:

• a collet sleeve for riding on an upright shaft, said collet sleeve having a radially outwardly projecting pin;
• a hub sleeve for attachment to a hub of said footring, said hub sleeve having a track for receiving said pin, said hub sleeve for riding on said collet sleeve:
• said track receiving said pin when said hub sleeve rides on said collet sleeve:
• said track having a spiral track section extending between a first pin stop and a second pin stop so that, with said collet sleeve riding on said upright shaft and said hub sleeve riding on said collet sleeve, said first pin stop is above said second pin stop such that downward spiral movement of said hub sleeve results in relative movement between said pin and track to move said pin to said first pin stop and upward spiral movement of said hub sleeve results in relative movement between said pin and track to move said pin to said second pin stop;
• at least one of an outer surface of said collet sleeve and an inner surface of said hub sleeve tapered such that when said hub sleeve is moved so that relative movement between said pin and track moves said pin along said spiral track section to said first pin stop, said hub sleeve is advanced downwardly on said collet sleeve to compress said collet sleeve onto said shaft to frictionally lock said collet sleeve to said shaft and when said hub sleeve is moved so that relative movement between said pin and track moves said pin along said spiral track section to said second stop, said hub sleeve is retracted upwardly on said collet sleeve to release compression of said collet sleeve so that said collet sleeve is slidable on said shaft.

A seat having an adjustable footring comprising:

• a support shaft;
• a collet sleeve riding on said support shaft, said collet sleeve having a radially outwardly projecting pin;
• a hub of said footring extending about said collet sleeve, said hub having a track receiving said pin, said track having a spiral track section extending between a first pin stop and a second pin stop so that said first pin stop is above said second pin stop;
• at least one of an outer surface of said collet sleeve and an inner surface of said hub sleeve tapered such that when said hub sleeve is rotated so that said spiral section of said track moves along said pin to said first pin stop, said hub sleeve is advanced downwardly on said collet sleeve to compress said collet sleeve onto said shaft to frictionally lock said collet sleeve to said shaft and when said hub sleeve is rotated so that said spiral section of said track moves along said pin to said second pin stop, said hub sleeve is retracted upwardly on said collet sleeve to release compression of said collet sleeve so that said collet sleeve is slidable on said shaft.