Heavy Split Lock Washer: Case Hardened, Black Oxide, Steel, 1 3/8 in Screw Sz, Case Hardened, 5 PK

Split-lock washers have a spring action that creates resistance against vibration. Also called spring-lock washers, they have an opening where one side gradually rises above the other, compressing while simultaneously pushing against the mating surfaces. They are available in various types, including high-collar split-lock washers, which are often used with socket head cap screws, and are often used with softer materials and do not provide as much resistance to loosening in harder materials. Case Hardened is a rating given to steel fasteners with flexible cores and hardened exteriors. Cased hardened fasteners are most commonly used in conjunction with Grade 5 fasteners. Black Oxide is a black coating that protects fasteners in dry environments.