are used under the head of 12 point high strength bolts (MS 21250-060XX) that may be used on the gear legs in place of the NAS6606 bolts Vans supplies. If you are contemplating this modification I have a deal for you! I had to order a minimum of 100 of these critters when I procured fasteners to accomplish this mod. Anyone that wants a set of 4 will be welcome to them, just PM me. I think four of them can make the one ounce wt. limit for 49 cents...