I got curious to see if the threads matched up with my 4Sevens Quark Pro 2A and my Fenix PD30 R4. Apparently, they do. Since the Quark is only rated to 4.2 volts, I obviously can’t use 2 123A cells in it without frying it. However, it does work perfectly fine on a 16650 lithium ion cell, which works better anyway. Now I can more easily pocket carry a Quark light and it will more likely have better runtime than two Eneloops AAs.