Made of steel, these won't fall out or come loose like plastic or aluminum with O-ringsFit tightly and add that special finishing touch to the top of an Allen boltAssortment kit includes a convenient tray with 100 each of the 1/4", 5/16" and 3/8" size chrome plugs, plus three sample Allen bolts with plugs installed as sales tools10-pack is display packaged with a poly bag for individual sale100-pack refill bags available to keep your assortment kit fully stockedMade in the U.S.A.NOTE: Sizes given are the thread size of the bolt not the Allen wrench area.