Features: 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. Specifications: Material:Carbon Steel Internal Diameter : 1/8",3/16",1/4",5/16",3/8",7/16",1/2" 5/8" (3, 4, 5, 6, 8, 10, 12,16mm) Surface treatment: Blackening treatment Package Includes: 2 Set of 8pcs Drill Limited ring Set with Wrench