Features: These self centering drill bits put hinges right where they should be in the center. The inside drill bit is made of HSS, high hardness, rustproof, solid and durable. Easy to use, drilling and tapping, high working efficiency. Positioning accuracy, will not shift, the chips will automatic discharge from the hole on either side of the top of the drill, not stuck drill. 6 of the most often used sizes for carpenters, cabinet, furniture makers and other wood working trades. Specifications: Material: HSS, Aluminum Size: approx. 5/64', 7/64',9/64', 11/64', 13/64',1/4' Weight: approx. 177g Opening size: 5/64': Opening diameter: approx. 2mm, needs approx. 2.2-2.8mm Self tapping screw 7/64': Opening diameter: approx. 2.8mm, needs approx. 3-3.5mm Self tapping screw 9/64': Opening diameter: approx. 3.5mm, needs approx. 4-4.5mm Self tapping screw 11/64': Opening diameter: approx. 4.5mm, needs approx. 5-5.5mm Self tapping screw 13/64': Opening diameter: approx. 5.1mm, needs approx. 5.6-6.1mm Self tapping screw 1/4': Opening diameter: approx. 6.3mm, needs approx. 6.8-7.3mm Self tapping screw Using Manual: According to the hardness of the wood to adjust properly, if the wood is soft, you can choose a small number, if the wood hard, you can choose the corresponding one or larger one. Package included: 6 x Self Centering Hinge Drill Bit