Black Washer - 3/8 ID x 5/8 OD (1)

The ARP Black Washer – 3/8 ID x 5/8 OD is a precision flat washer engineered for general-purpose fastening applications where load distribution and corrosion resistance are essential. Flat washers serve as critical spacers and load spreaders in mechanical assemblies, reducing stress concentration under bolt heads and nuts while protecting underlying surfaces from damage. This single-unit washer is ideal for builders, mechanics, and technicians working on firearms, machinery, or structural projects who demand reliable, long-lasting fastener components.

Manufactured from hardened steel and finished in black oxide coating, this washer delivers superior corrosion resistance and a professional appearance suitable for both indoor and outdoor use. The black oxide surface treatment protects against rust and oxidation while maintaining a uniform matte finish that resists glare and blends seamlessly into tactical and precision assemblies. With an inner diameter of 3/8 inch and outer diameter of 5/8 inch, the washer provides optimal bearing surface for M10 fasteners, distributing clamping forces evenly across larger surface areas to prevent fastener pull-through and material deformation.

This black oxide flat washer is compatible with standard metric and imperial bolt applications, making it suitable for AR-15 build kits, precision rifle work, industrial machinery, and general hardware assembly. The 0.063-inch thickness provides adequate rigidity for high-pressure applications while remaining lightweight at just 0.01 pounds. Whether upgrading firearm components, securing optic mounts, or assembling critical fastening systems, having premium-grade black oxide washers on hand ensures professional-grade results and long-term reliability in any demanding application.