As shown. 2 Barbed Half Moon Washers for Vintage Gibson Truss Rods. Help for Old Truss Rods. If Your Gibson Truss Rod Half Moon Washer has gone missing or is rotated and you want to replace it,here you go ! These were developed by Stu Mac to fit Gibson guitars. The barbs keep the washer from shifting around (rotating). You can also file off the barbs and double stack your washers to get a bit more adjustment out of your truss rod.  Careful though,truss rods do break so if you are not comfortable doing adjustments,bring it to a trusted shop.