The collet holder is a steel square block with a nut to draw in a collet. When used with the saw table it offers a fast method of slotting screw heads, milling squares and numerous other operations. You can select the nut thread pitch standard WW size to fit most lathe as Levin, or metric size M7 x 0.75, such as Vector and HOROTEC German brand. Pictures for refeence only.  Collet is not including on this auction.