KAC-Knight's Armament Receiver Extension/Sling Mount Castle Nut

KAC-Knight's Armament Receiver Extension/Sling Mount Castle Nut (21496-1)

Replacement buffer tube/sling mount castle nut for the Knight's Armament Sling mounts, part numbers 22051-1 and 24103-1. 

Current version for 2021, uses a standard armorer wrench for install.