PSI Woodworking L5818 Headstock Spindle Adapter (Shopsmith 5/8-Inch to 1-Inch 8tpi chuck)
Converts your Shop Smith lathe spindle so that you can use chucks with a 1" x 8 tpi thread size.  Adapts to your 5/8-inch no thread spindle to accomodate any 1" x 8 tpi female mount accessory.  Made of steel, and has set screw to tighten to the flat on the spindle.  Extends the spindle length over 1-inch.