Drill Warehouse Drill Stop Bit Collar Set &ndash; Kit Includes: 1/8", 3/16&rdquo;, 1/4&rdquo;, 5/16&rdquo;, 3/8&rdquo;, 7/16&rdquo;, 1/2&rdquo; and 5/8&rdquo; Inch with Allen Wrench to Tighten the Stops Set-Screws (8-Piece) Material:Carbon Steel Internal Diameter : 3mm,4mm , 5mm , 6mm , 8mm , 10mm , 12mm, 16mm 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