MTE Limited part number 01 000854 001 (01-854-11) Round Pushbutton Stay-Put Hand Release type 33 mm. This is the top manual section and not the switch mechanism.  

Pushing the button will lock the mechanism in the engaged position. Turning the hand-release ring will disengage the mechanism.

Item is in original box from old stock (NOS). and is unused (no markings or blemishes). Box cardboard exterior shows signs of age consistent with extended storage and tears have been re-taped.