These are Corby Bolts. They are used for knife handle fasteners. With this design, you will create a step hole in your handle material that is slightly larger than the shank of the fastener. The two-part assembly allows for you to pass the shank precisely through your knife tang hole and handle material, allowing the larger radius of the Corby Bolt heads to create a pinch point on both sides of the handle material, where it can then be tightened down to a secure hold. Once the bolt has been tightened, it can be sanded to a flush finish with the handle surface. This will result in a smooth, pin-like visual effect on the final knife handle. When used with epoxy and/or thread-locker adhesive, Corby Bolts will create a permanent knife handle bond.