This diffuser fits snugly onto the Thrunite TN4A.

The print has small beads along its base that will allow it to lock into place along the first or second groove of the flashlight. It will be hard to place at first but as you insert and remove the diffuser the beads will wear down to a perfect fit. They are designed to be larger than needed for long term use.

When installing, you should hear a slight "pop" when it locks into place.