Abstract: In a device of the type having a rotatable operating member for purposes of selective adjustment thereof, a locking structure for selectively locking the device in predetermined positions. The locking structure has a lock plate affixed to the device and includes a locking portion therein. A separate lock tab member is closely received on the operating member and has a tab portion including a third locking hole which will register with one of the first and second locking holes when the operating member is moved to the predetermined positions in order that a locking member may then be passed through the aligned locking holes. Stop members included on the lock tab coact with the device itself to define the extreme rotated positions of the operating member. A handle is closely received over the operating member for conveniently rotating the member and advantageously extends in generally the opposite direction from the tab portion of the lock tab.