This is the Leatherman Carbon Scraper for the Mut Multi-Tool. This item is used to remove the carbon build-up from your M16/AR15 that results from the gas system in these weapons. When the carbon builds up, it degrades the performance of the rifle.
This accessory is used to rid the bolt, carrier and firing pin of this build up. The beauty of this item is that the surface area is large enough to cover all areas of the bolt assembly.