Shank - 0.125 (1/8) inch or 3.17 mm, Length - 1.425 (1 13/32) inch or 36.19 mm Mandatory for DIY tree with rotating tree tool. As long as you follow the recommended rotations for wood species, you shouldn't have any problems. Btw I used my calipers to measure the drill and regret not spending extra on digital models. So if you don't have perfect eyesight, spend a little more on digital models!