Held in the adjustable tailstock holder P/N 1203 (not included) you can now hold extremely small drills, accurately on center. Drills of only a few thousandths of an inch are easily broken if not perfectly centered. The WW collet adapter holds Sherline WW collets that have a shank diameter of .312-.313″. Other manufacturers make collets that vary in size up to .314-.315″. The 8.0 mm adapter is made to hold collets of that size. If your collets are not made by Sherline, measure them carefully to see which adapter you should use.