the american one has a little lip on. so it clips in. then it swings round like a strat trem arm.
like i say, you couldn't just put an american arm in a japanese collet. it would be too small. but maybe you could put an american collet on a japanese lever after all, though. if the thread on the american collet is small enough to go through the japanese lever, you could then put a nut on the other side, to fasten it. it could be that the threads are the same size though, i dunno. usually, american and japanese thread sizes are different. usually due to imperial/metric measurements
