Drill Warehouse 7 Pcs General Tools & Instruments Bit limit ring - 3,4,5,6,8,10,12mm Drill Stop Assortment for Drill Bits Consistent Drilling (One Set of 7) Material:Carbon Steel Internal Diameter : 3mm,4mm , 5mm , 6mm , 8mm , 10mm , 12mm Mainly for fixing the drill bit,limited the depth of drill holes,make depth of the hole consistent. Works with both standard and brad-point bits Setscrew type collar will not damage bits