Internal Tooth Lock Washer: Case Hardened, Zinc Plated, Steel, #4 Screw Sz, Case Hardened, 100 PK

Tooth lock washers have teeth around their outer or inner diameter that grip onto surfaces. Washers with external teeth are used with larger screws or bolt heads. Washers with internal teeth are commonly used in electrical applications, where they scrape the surrounding area to enhance the electrical connection. Countersunk lock washers have a concave shape with teeth designed to prevent slippage and absorb shock and vibration. 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. Zinc Plated is a zinc coating that makes fasteners corrosion-resistant in wet environments.