An adjust and lock mechanism includes a drive gear (16) rotatably mounted on a frame and adapted to engage a drive track (15) on a member (13) to allow adjustment between the frame (1) and the member by rotation of the drive gear, the drive gear being mounted on a drive spindle (17) that can move axially relative to the drive gear and which is normally spring loaded (34) into locking engagement with the frame and can be moved axially to disengage the locking engagement and allow the spindle to be rotated to operate the drive gear. A locking engagement is provided by a dog gear at one end of the spindle. A lock release button (32) and hand wheel (18) to rotate the drive gear are located adjacent one another for joint operation. A gear train connects the hand wheel to the drive gear.