These Krebs Custom Vadapter Block adapters are shaped and contoured to fit most Yugoslavian rifles. Made of 6061-T6 aluminum that's been hard-coat anodized, they're designed to allow owners of Yugoslavian rifles to mount alternative buttstocks on their rifle. Includes installation screw & lockwasher. NotesScrew should be installed from the inside of the receiver to the adapter.Will not fit slant back receivers. Some rifles may require a modified block if rivets are protruding.