These protective screw on end caps are compatible with both the Hakkatsu Thunder B and Valken Thunder V Cylinder C style threaded shells. These reusable caps protect the edges of the grenade from the impact of being thrown which can cause gas to leak from the shell and prevent it from detonating. They also reinforce the ends from blowing out and can add a few extra seconds to the timed detonation. These top and bottom caps are made from high impact polymer and are completely reusable.