This is a drilling depth gauge associated with the AR-15 80% Lower Receiver Milling Jig https://odysee.com/@Sp0z3n:7/AR-15-80-Universal-Lower-Receiver-Milling-Jig:a This gauge will assist with proper depths while milling out a billet. The alterations I used on this jig from @AreWeCoolYet was this is just the depth gauge portion of the top plate. Link to the original here - https://odysee.com/@AreWeCoolYet:7/80percentRouterJig:b