I think it screws down and locks, you may have to unscrew the locking knob to get it to release. Going from memory here, I'll go check mine to confirm.
Knob does screw down and lock, once unscrewed (loosened) you have to push down on the knob to release. Mine seems to have a "front and back", if I put the adapter on one way it works well, turn it around and it is harder to get off. Go figure...
-Doug
Last edited by DesertBighorn; 06/17/15.