My Bosch angle grinders have been retro-fitted with FIXTEC brand tool-free nuts which may be similar to the OP's; they do, however, have a flip-up half-moon feature which I don't see in the photo.
Long term users of the Tormek wet grinder will know that their original nuts had to be hammered tight but later models feature an ingenious two-start left hand threaded nut which is easily removed by hand.