Flat Washer Plain Washer Class 4 8 10 SS304 SS316 Zinc HDG (DIN 125 / ISO 7089)

The Flat Washer (commonly referred to as a plain washer, circular washer, fender washer, structural hardened washer, or DIN 125 / ISO 7089 fastener) is an essential load-distributing mechanical component placed under the head of a bolt or underneath a hex nut. By providing a smooth, flat bearing surface, the washer spreads the clamping force across a larger surface area, preventing damage to connected mating materials, bridging oversized holes, and preserving uniform joint pre-load. Manufactured in carbon steel (Standard 100HV/140HV and High-Strength Hardened 200HV/300HV/ASTM F436) and austenitic stainless steel (SS304/A2 and SS316/A4), our flat washers comply strictly with global ISO standards.

Technical Specifications of Carbon Steel & Stainless Steel Flat Washers

We supply a complete range of washer dimensions and strength grades, including standard DIN 125 Form A (without chamfer), DIN 125 Form B (with chamfer), DIN 9021 large outer diameter fender washers, and ASTM F436 heavy structural hardened washers for high-tensile steel construction.

Precision Stamping and Thermal Heat Treatment Process

At our manufacturing facility in Handan, China, flat washers are produced using high-speed automated multi-stage stamping presses, thermal hardening furnaces, and surface finishing lines:

• High-Precision Coil Stamping: Premium strip steel coils pass through automated stamping dies that blank the outer diameter and pierce the central hole simultaneously to ensure excellent concentricity and flatness.
• Vibratory Barrel Deburring: Blanked washers undergo ceramic media tumbling to remove sharp stamping burrs, establishing smooth bearing surfaces that protect mating parts.
• Thermal Hardening & Tempering (High Strength / ASTM F436): Medium carbon and alloy steel washers are heat-treated in continuous atmosphere-controlled furnaces to reach uniform 200HV–300HV or 38–45 HRC hardness without warping.
• Surface Coating & Chemical Passivation: Electro-zinc plating (5–12 µm), Hot-Dip Galvanizing (45–85 µm molten zinc dipping), or acid passivation for stainless steel washers.

Essential Engineering Applications of Flat Washers

Flat washers are fundamental components utilized across every structural, industrial, and mechanical assembly:

• Structural Steel Construction & Bridges: ASTM F436 hardened washers paired with heavy hex structural bolts on bridge girders and steel building frames.
• Power Transmission Line Towers & Overhead Hardware: Hot-dip galvanized flat washers used on cross-arm assemblies and substation gantries to resist severe outdoor weather corrosion.
• Automotive, Industrial Machinery & Furniture Assembly: Electro-zinc plated and stainless steel washers installed under bolts to prevent surface cracking and gouging on soft sheet metal or plastic housings.

Quality Control and Export Packaging for Flat Washers

Handan YiHao Fastener enforces strict Quality Assurance (QA) standards for all overseas export orders. Testing procedures include 100% inner/outer diameter plug and ring gauge checks, micrometer thickness verification, Vickers/Rockwell hardness testing, and salt spray validation.

All export items are bulk packed in heavy-duty 25kg inner cartons, neatly stacked on ISPM 15 compliant fumigated wooden pallets, and wrapped in protective stretch film for safe ocean freight.