ARP Washer

ARP Washers: Precision Hardware Built for High-Performance Builds

When engine builders and fabricators trust ARP (Automotive Racing Products) for their most critical fasteners, it only makes sense to complete the assembly with washers engineered to the same uncompromising standard. ARP washers are far more than an afterthought — they are purpose-built components designed to distribute clamping loads evenly, protect mating surfaces, and maintain the integrity of a fastener assembly under the extreme heat cycles and vibration loads that performance engines produce.

Materials and Finish Options

ARP's washer lineup is built around two core material choices that performance builders already know and trust. Polished stainless steel offers excellent corrosion resistance and a clean aesthetic, while black oxide–treated 8740 chrome moly delivers the toughness demanded in race engines and high-load diesel applications. Both materials are produced and finished entirely in-house at ARP's Southern California facilities, where metal finishing operations include black oxide coating of chrome moly and polishing stainless steel to a brilliant luster — the same quality-control environment that governs every ARP fastener.

SAE, Metric, and Insert Washer Types

ARP covers a broad spectrum of applications with SAE sizes ranging from 1/4-inch to 3/4-inch, as well as metric sizes from M6 through M18, ensuring compatibility with virtually any domestic or import performance build. Within the lineup, builders can choose between standard and chamfered versions — chamfered designs are specifically intended for use under bolt heads, allowing the washer to seat cleanly against a fastener without introducing stress concentrations.

One standout offering in the ARP washer family is the Insert Washer. These fully CNC-machined, through-hardened 8740 chrome moly pieces feature a special snout (or insert) that fits into the top of a bolt hole, protecting the surrounding material from galling or collapsing — a critical concern in high-load applications and any area that sees repeated disassembly and reassembly, such as cylinder head studs in competition diesel or racing engines.

Parallel-Ground for Uniform Clamping

ARP's special-purpose washers are hardened and parallel-ground, meaning both faces are machined to be precisely flat and parallel to each other. This seemingly simple detail matters enormously in practice: a washer that isn't truly flat introduces uneven clamping loads that can skew torque readings, leading to inconsistent preload across a fastener assembly. For builders who are torquing head studs or connecting rod bolts to exacting specifications, a parallel-ground washer ensures that the clamping force applied goes exactly where it is intended.

Completing the Full Fastener Assembly

ARP washers are designed to complement the brand's legendary bolts and studs, allowing builders to source an entire fastener assembly — bolt or stud, nut, and washer — from a single manufacturer with consistent material properties and dimensional tolerances. Whether you are building a custom combination from ARP's bulk fastener offerings or pairing washers with application-specific kits, the result is a unified hardware package that meets the same stringent standards trusted in NASCAR, Formula 1, IndyCar, and NHRA competition.

• Material options: polished stainless steel and black oxide–treated 8740 chrome moly
• SAE sizes from 1/4" to 3/4"; metric sizes M6 through M18
• Standard and chamfered styles available
• Insert Washers protect hole tops from galling and collapsing
• Hardened and parallel-ground for uniform clamping load
• Available individually (bulk) or in 2-pack and 10-pack quantities
• Produced and finished in-house at ARP's Southern California facility