Note: Only accepts 1/4 inch shank bits. Need to tighten with a wrench to prevent the bit from falling off. Made of heavy-duty steel, can be used for clamping 1/4 Inch shank drill,milling cutter, straight shank tool. Shank diameter: 1/4/ 6.35mm, Hold diameter: 1/4"/6.35mm; Overlength: 3.15"/ 80mm. Eliminates the dangerous temptation to withdraw the shank from the collet. Extend the bit to provide the full depth of cut. Suitable for automobile manufacturing, mold manufacturing, machinery manufacturing and so on. Note: It's need to use a wrench to tighten. Specifications: Material: Heavy-duty Steel Shank Diameter: 1/4 Inch Hold Diameter: 1/4 Inch Overall Length: 3.15 Inch Suitable for: woodworking trimming, milling, engraving machine. Please Note: The tool extends the length of the chuck as short as possible, the tool extends the amount of time longer; If extended, please cut their own speed, feed rate or cutting the amount. Package Included: 1 x Router Collet Extension