David, A lot of the older lens mounts/adapters available many years ago were built the same way. I've always done like you suggested and stuck a very narrow bladed screw driver into the slots and twisted them open. Some will stay tight longer than others, but beware that some of the flange/mounts are made of soft, or brittle type metals and do develop stress cracks if nudged too much. (Don't ask how I know this). Art Tafil