once you take some plyers to bend out the teeth on it, this cap just pops in and out easily without fallin out when you don't want it to. i WAS a TINY bit disappointed that it doesn't fit perfectly flush with the tube but that's no big deal. i was also hoping to stick a d ring on it but that's NOT a good idea because it would definately pop right out. it does however also provide a good way to mount a 4 aaa battery pack by bending the teeth around the bottom of it