Drilling with forstner bits to achieve a flat bottom hole or to start a deep hole turning project like on a larger vase or vessel is essentially impossible with a standard length forstner bit. To remedy this issue we have developed a heavy duty steel extension that allows you to secure a 3/8 inch shank forstner bit into the end collet. The forstner bit extension gives you additional 5-5/8 inches of reach to bore deeper into your projects. This will help you create larger diameter starter holes or help when you need to drill in just a little further than the standard bit length will allow. The extension can be used with forstner bits on drill presses, lathes with a drill chuck installed (drill chuck not included) or with a power drill. One of the most common uses for the forstner bit extension is for woodturners who need to bore out starter holes on larger vessels. However, the extension works exceptionally well for projects like salt shakers, pepper mills or even wood turned beverage mugs. Contractors use the extension when they need to bore deep holes for running cables or wires and they also use it for joining larger timbers. The forstner bit extender is made from solid, heavy duty machined steel. It is designed to be used with forstner bits only. The collet inside diameter is 3/8 inch. This tolerance is very tight and designed to accept forstner bits with shank sizes of 3/8 inch or slightly smaller. Please note that some forstner bit manufacturers produce bits that say 3/8 inch shank size when in fact they are not. If you measure your bit shank and it is 3/8 inch, your bit should fit once the set screws are loosened. The collet outside diameter is 25/32 inch without the set screws protruding outward. The reason this is important is that as we mentioned earlier, some bits may have slightly different shank sizes. This means the set screws may protrude outwardly from the collet. The minimum size hole this extension will allow you to drill is 13/16".