Concave Convex Washer

Concave Convex Washer — Spherical & Curved Alignment Washer | Self-Aligning Design | Angular Compensation

Concave convex washers (also known as spherical washers or self-aligning washers) are precision-engineered washers consisting of a matched pair — one with a concave (inward-curved) surface and one with a convex (outward-curved) surface mating together. This spherical interface allows angular adjustment and self-alignment of the bolted connection, compensating for non-parallel surfaces and preventing bending stress on the bolt. Manufactured to industry standards, our concave convex washers are essential for applications requiring precise alignment, angular compensation, and even load distribution on irregular or angled surfaces.

Material & Specifications

Size Range	M6 to M36 / 1/4″ to 1-1/2″ (bolt diameter)
Standard	DIN 6319 (Spherical Washers, Type C & Type D), GB/T 849, ISO 10673, Custom Specifications
Material	Carbon Steel (Grade 8.8/10.9 compatible), Alloy Steel (42CrMo / 40Cr), 304 Stainless Steel (A2), 316 Stainless Steel (A4), Case-Hardened Steel
Surface / Coating	Hot-Dip Galvanized (HDG), Electroplated Zinc Blue/White, Color Zinc/Yellow, Dacromet, Multi-Element Alloy Co-Permeation, Black Oxide, Phosphated
Hardness	HRC 35-45 (mating surfaces hardened and polished for smooth articulation)
Angular Compensation	Typically ±3° to ±5° (depending on size and design)

Surface Treatment & Zinc Coating Quality

At BoltNutsPlus, we understand that surface treatment is critical to fastener longevity and performance. Our washers undergo rigorous coating processes to ensure maximum corrosion resistance and durability. We offer five premium coating options, each tested to international standards:

• Hot-Dip Galvanizing (HDG) — Thick zinc layer (50-120μm) providing superior long-term corrosion protection for outdoor, marine, and industrial environments. Compliant with ISO 1461 / ASTM A153 standards. Salt spray resistance: 500-1,000+ hours. HDG washers are ideal for structural steel assemblies exposed to harsh weather.
• Electroplated Zinc Blue-White (Zn Blue/White) — Bright, clean silver-blue appearance with 5-15μm zinc layer. Cr3+ passivation technology, fully RoHS compliant. Ideal for indoor machinery, electronics, and general-purpose applications requiring aesthetic appeal and moderate corrosion resistance.
• Color Zinc / Yellow Zinc (Iridescent Passivation) — Multi-colored iridescent passivation film offering enhanced corrosion resistance (100-200 hours salt spray) with a distinctive golden finish. Widely preferred in automotive, agricultural equipment, and construction machinery sectors for its balanced protection and visual appeal.
• Dacromet Coating — Advanced water-based zinc-chromium coating technology with NO hydrogen embrittlement risk. Provides 1,000+ hours salt spray resistance, making it the preferred choice for high-strength fasteners in extreme environments. Environmentally friendly (no heavy metal discharge), RoHS/ELV compliant, ideal for automotive and wind energy applications.
• Multi-Element Alloy Co-Permeation — Zinc-aluminum-rare earth alloy layer offering 2-3x the corrosion resistance of traditional galvanizing. Features self-healing properties at scratch points, ensuring long-term protection even in damaged areas. Ideal for critical infrastructure, power transmission towers, coastal projects, and marine installations.

Key Features

• Spherical mating interface enables automatic self-alignment, compensating for up to ±5° of angular misalignment between bolted surfaces
• Matched concave-convex pair distributes clamping force evenly across the spherical contact area, eliminating point loading
• Prevents bending stress and fatigue failure in bolts caused by non-parallel clamping surfaces
• Polished mating surfaces with optimal surface finish ensure smooth articulation and consistent preload transfer
• Case-hardened contact surfaces (when specified) resist brinelling and wear under high clamping forces
• Essential component for fixtures, tooling, die sets, and any application requiring precise angular alignment

Applications

• Injection molding machines, die casting machines, and press tooling with non-parallel mounting surfaces
• Machine tool fixtures, clamping systems, and workholding devices requiring precise component alignment
• Heavy machinery mounting on uneven or sloped foundations — prevents bolt bending and base plate distortion
• Clamping systems for irregular workpieces, castings, and fabricated assemblies in machining centers
• Bridge bearing assemblies and structural movement joints allowing angular rotation
• Test fixtures, measurement equipment mounting, and precision alignment applications in laboratory settings

Why Choose BoltNutsPlus?

• ISO 9001:2015 Certified Manufacturing — consistent quality you can trust on every batch
• 15+ Years of Export Experience — serving 40+ countries across 6 continents
• Full Traceability — material certificates (EN 10204 3.1) and comprehensive test reports included
• Custom Packaging & OEM/ODM — your brand identity, your specifications, our precision manufacturing
• Third-Party SGS / Bureau Veritas Inspection Available upon request
• 24-Hour Quote Response — same-day reply for urgent requirements; standard 24-hour turnaround