This is a hopper adapter for the nerf gelfire line. It fits really snugly into the blaster's existing port (may need some sanding) by both friction and the locking system designed in the blaster. The adapter can be inserted so that the hopper can be angle to either side to improve the user's sight picture.

The hoppers fit into the adapter by purely friction fit. They may rattle slightly but they should stay in under rough play.