Our 3 and 4 Jaw chucks are available in two sizes, 2.5″ and 3.1″. They are available with 3/4-16 threads for use on Sherline machines. The smaller 2.5″ chucks are available with other spindle threads to fit machines made by other manufacturers, such as 12 mm x 1 mm and 14 mm x 1 mm for older Unimat lathes or 1/2-20 for old 6″ Sears lathes.