These are Loveless Fasteners. They were introduced by knife making legend, Bob Loveless, and are used for affixing knife handles. Loveless Fasteners are a 3-piece design and include (2) threaded heads and (1) threaded screw. With this design, you will create a step hole in each side of your handle material that is slightly larger than the shank of the threaded screw. The three-part assembly allows for you to pass the threaded screw precisely through your knife tang hole and handle material, allowing the larger radius of the Loveless fastener heads to create pinch points on both sides of the handle material, where it can then be tightened down using the screw slot to a secure hold. Once the threaded heads have been tightened, the screw head can be removed and the assembly can be sanded to a flush finish with the handle surface. This will result in a very attractive final surface that resembles a bull’s-eye. Using different materials for both screw and heads will further the contrast of the effect. When used with epoxy and/or thread-locker adhesive, they will create a permanent handle bond.