Made of premium quality high speed steel with high hardness and durability, anti-rust. These square drill hole bits are suitable for construction, installation, renovation,decoration industry, etc.Specifications:Clamping cylindrical diameter: 19mmType: 9.5mm(3/8"), 8mm(5/16"), 12.7mm(1/2"), 11mm(7/16") (optional)Drill core: 9.5mm(3/8"), 8mm(5/16"), 12.7mm(1/2"), 11mm(7/16") (optional)Package size: 230 * 35 * 35mmPackage weight: about 220gNote:1. Please allow 1-3mm differs due to manual measurement.2. Due to the different display and different light, the picture may not reflect the actual color of the item. Thanks for your understanding.3. Square hole drill can not be used on an electric drill, drill square holes need to fit a square hole drill drilling (mortise and tenon machine) to use.4. In case drill bits become overheated and get burned up due to fast rotary friction,we suggest use some cutting fluid to keep the bits cold during usage.Packing List:1 * Square Hole Drill