This high-quality, geared drill chuck is designed exclusively to work with all Shopsmith MARK models. Accommodates any bit between 0.020 and 1/2-Inches. This Drill Chuck is standard equipment with the 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. Includes (1) 1/2-Inch Drill Chuck (501420) and (1) Drill Chuck Key (501419).