3,4,5,6,8,10,12mm Carbon Steel Drill Depth Stop Collars Dowels Chuck +Hex Wrench General Tools & Instruments Bit limit ring Material:Carbon Steel Specification:3,4,5,6,8,10,12mm Mainly for fixing the drill bit,limited the depth of drill holes,make depth of the hole consistent Hex wrench is included for tightening the stop precisely on the drill bit