PSI Woodworking LA341018 Headstock Spindle Adapter (3/4-Inch x 10tpi to 1-Inch x 8 tpi chuck)
Converts your lathe spindle so that you can use a chuck with a different thread size.  Adapts a spindle thread of 3/4" x 10 tpi to a 1" x 8 tpi male thread to accommodate a variety of chucks. Made of steel, with two flats to allow you to use a wrench when tightening. Permits the use for any 1" x 8 tpi  accessory.  Extends the spindle over 1-inch.