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

The S/S Flat Washer - 3/8 ID x 5/8 OD from ARP is an essential fastener component for any serious engine builder or performance mechanic. These precision stainless steel washers distribute clamping force evenly across bolt heads and threaded components, preventing surface damage and galling during assembly. Whether you're building a stroker motor, upgrading cylinder head bolts, or securing intake manifolds, flat washers are non-negotiable items in your fastener arsenal for professional-grade results.

Manufactured from premium stainless steel, this washer features a 3/8-inch inner diameter (ID) and 5/8-inch outer diameter (OD), making it ideal for 3/8-inch fasteners commonly found in high-performance engine applications. The flat design eliminates stress concentration points and ensures uniform load distribution across the clamping surface, a critical consideration when working with aluminum heads or composite materials prone to distortion. ARP's engineering standards guarantee consistent thickness and dimensional accuracy—properties that prove essential when torquing fasteners to specification in performance builds where fractions of a millimeter matter.

Mechanics upgrading factory fasteners to ARP studs and bolts will find this washer compatible with their entire assembly strategy, particularly in applications requiring high clamping loads such as water pump mounting, alternator brackets, and accessory drive systems. Stainless steel construction resists corrosion in underhood environments and delivers superior longevity compared to zinc-plated alternatives, especially in forced induction or high-heat applications. For single or bulk purchase, this washer delivers the reliability and precision fit that separates amateur modifications from competition-ready engine builds.