I am having the exact same issue from above with my new Brevis/ Nikon lens mount.
None of my lenses fit tightly on the adapter. I can wiggle and rotate them all. They're on there, but not tightly. Lots of play.
I feel like if I tilt my camera down, the whole lens will fall off!
I've tried the rotation all the way around, and the pin is lined up properly.
It feels like the lens mount grooves are too deep for the actual lens threads.
Brevis Revision 2
Rails and adjustable rail mount
Nikkor 50mm f/1.8
Nikkor 105mm f/2.5
Vivitar 85-205mm f/3.8