1. Material: aluminum alloy + nylon 2. Nylon inner ring, easy to lock, not loose, and effectively avoid wear on the locking part of the drill bit 3. The outer ring is made of aluminum alloy, which is durable, beautiful and light 4. Anti-slip texture on the surface, can be tightened manually, simple and practical 5. The inner diameter of the stopper can be adjusted, one at the top, and can be fixed at different positions of the drill bit to accurately control the drilling depth 6. Diameter: about 20mm for type 2-5, about 28mm for type 6-11
