Atoplee 3pcs Self Centering Vix Bit Hinge Wood Drill bit Tool Set, 5# 9# 12# Material: brass, high-speed steel 5# opening diameter :about 2.8mm,Please using the self-tapping screw(about 3-3.5mm) 9# opening diameter :about 3.5mm,Please using the self-tapping screw(about 4-4.5mm) 12# opening diameter :about 4.5mm,Please using the self-tapping screw(about 5-5.5mm) These self centering drill bits put hinges right where they should be in the center