This high-quality geared drill chuck is designed exclusively to work with all MARK models. Accommodates any bit between .020 and 1/2 Inches. Standard Equipment with a new MARK 7. Easily mounts to the quill spindle with a single setscrew. Buy additional Drill Chucks and Keys for commonly used drill bit sizes. No need to unlock and remove the drill bit, simply loosen the single setscrew and change the entire Chuck with drill bit. Lose Your Drill Chuck Key or want to Keep a Spare? No problem, buy an extra Drill Chuck Key Separately (501419).