Designed for assembly around a high-strength hardened steel bolt (Grade 8 and above) between the bearing surface of the fastener and what it is attached to, these thru-hardened flat washers are used to improve stress distribution. They have tighter tolerances on thickness than a Low Carbon flat washer, and have slightly smaller inside and outside diameters than its USS counterpart. SAE washers were created to serve similar purposes as USS washers, but specifically meet the requirements in the automotive engineering field. FW78F8