The KNS AR15 Perma Pin Retaining Firing Pin (PERMA) replaces the standard cotter pin found in the bolt carrier to retain the firing pin as in original Stoner rifles.
Instructions: Install the Perma Pin with the slot in the pin horizontal - with the length of the bolt. Align the Perma Pin with both holes in the bolt carrier and press the pin in. The pin will seat itself and become easier to install and remove with continued use.
Note: The pin may be broken if it meets rough ridges in the carrier holes and excessive force is used. Lightly remove any ridges with a round machinist file.