The package includes 1 square hole drill bit adapter, and 7 square hole drill bits. The drill diameter includes 1/4 inch (6.4mm), 5/16 inch (8mm), 3/8 inch (9.5mm), 1/2 inch (12.7mm), 9/16inch (14mm), 5/8inch (16mm), 3/4inch (19mm). The hand drill clamp diameter from 38 to 55mm/1.5 to 2.2 inch. Note: It is only suitable for bench drills and hand drills with clamps. The square hole drill bit adapter is crafted from carbon steel , sturdy and , which can hold wood firmly. It is about 6.3inch/16cm long, the upper inner diameter is about 0.75inch/1.9cm, and the lower diameter is about 2.17inch/5.5cm, reducing the use error. The drill bit not be blocked by sawdust, which has high hardness, not roll, and has fast cutting speed. It is , please take it out safely. The square hole drill bit adapter and drill bit set is easy to use. The design of the drill mortise attachment ensures you can drill the correct mortises and tenons in the fastest way. It is more convenient and fast than mortise machine. The dual support bracket is reliable and practical, suitable for bench drills and hand drills. It is perfect for woodworking, furniture manufacturing and other related industries. You can combine the square hole drill bit adapter with 7 square hole drill bits and this simplifies the process of drilling square holes on wooden boards. It fits for construction, woodworking DIY, decoration industries, materials with lower hardness such as compressed board, plastic, density board, sandalwood, pine, ash, pine, etc. Colour:Silver Material:steel Package Contents: 1set * drill adapter for hand drill Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.