1. Extends any Forstner shank bit an additional 83/4 inches, Helps you use standard forstner drill bits drilling for flat bottom holes or start deep hole turning projects like on larger vases or containers; 2. The collet inside diameter is 3/8 inch(9.7mm). This tolerance is very tight and designed to accept forstner bits with shank sizes of 3/8 inch or slightly smaller; 3. Highcarbon steel construction, precision ground and polished, ensuring it's sturdy and durable; 4. Two set screws and hex key included. To fasten the shank in place, use the hex key to tighten these screws; Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.