DIN 125A Flat Washer | ISO 7089 Plain Washer Marine Grade

DIN 125 Form A / ISO 7089 plain flat washer, size range M1.6 to M64. Manufactured in carbon steel ( Grade 4.8/8.8/10.9 matching ), stainless steel A2-70 ( AISI 304 ), and A4-70 ( AISI 316 ). Surface treatment: plain, zinc plated, or hot-dip galvanized. SINOFASTENER supplies DIN 125A flat washers with full dimensional compliance per ISO 7089, material traceability per EN 10204 3.1, and 36 years of marine fastener manufacturing experience.

What Is a DIN 125A Flat Washer?

ADIN 125A flat washer ( equivalent to ISO 7089 ) is a plain, disc-shaped washer with a central hole, used between the bolt head or nut and the clamped surface in a bolted joint. The"Form A"designation indicates normal series dimensions with a standard hole diameter slightly larger than the nominal bolt diameter. The washer distributes the clamping force over a wider area, protecting the joint surface from indentation, reducing contact stress, and compensating for slightly oversized holes.

In marine and shipbuilding applications, flat washers are essential components in virtually every bolted connection throughout the vessel. They are used in engine room piping flanges, hull structural connections, deck equipment mounting, and mooring system assemblies. The DIN 125A form is the most widely specified plain washer in general engineering, distinguished from DIN 125B ( which has the same dimensions but a different tolerance grade for product grade C ).

Marine Applications

Note: Application suitability based on material selection per ISO 3506-1 (stainless) or ISO 898-1 (carbon steel) and environmental conditions per industry practice.

Specifications and Materials

DIN 125A / ISO 7089 Dimension Table (Selected Sizes)

All dimensions per ISO 7089 Table 1. Full dimension table available upon request. Custom sizes and materials per shipyard specification.

Why Choose SINOFASTENER for Flat Washers?

Standards Reference

FAQ

Q1: What is the difference between DIN 125A and DIN 125B?

Both DIN 125A and DIN 125B share the same dimensional table (inside diameter, outside diameter, and thickness are identical). The difference lies in the product grade: Form A is product grade A with tighter tolerances per ISO 4759-1, suitable for precision applications. Form B is product grade C with wider tolerances, typically used in general-purpose applications where exact fit is less critical. For marine structural and piping connections, Form A is the standard specification.

Q2: When should I use a stainless steel flat washer versus a carbon steel washer?

UseA4-70 stainless steel washers (AISI 316/316L) when the bolted joint is exposed to seawater, ballast water, or chloride-containing environments, or when paired with stainless steel bolts to prevent galvanic corrosion. Use A2-70 washers (AISI 304) for less aggressive environments such as interior engine room applications. Use carbon steel washers (zinc plated or hot-dip galvanized) for general structural connections where corrosion risk is lower or where HDG coating provides adequate protection per ISO 1461.

Q3: Can DIN 125A washers be used with ASTM standard bolts?

Yes. DIN 125A / ISO 7089 is dimensionally compatible with ASTM inch-series bolts. For example, a DIN 125A M12 washer (d1 = 13.0mm, d2 = 24mm) pairs correctly with M12 hex bolts per ISO 4014/4017. For inch-series ASTM bolts (e.g., 1/2"UNC), refer to ASME B18.22.1 for the equivalent plain washer dimensions. SINOFASTENER supplies both metric (DIN/ISO) and inch (ASME/ANSI) flat washers.

Q4: Do you supply flat washers with hot-dip galvanized coating?

Yes. Carbon steel DIN 125A flat washers are available in hot-dip galvanized finish per ISO 1461, with typical coating thickness of 45-85 micrometers depending on washer size. HDG washers are commonly specified for hull structure and deck equipment connections where long-term corrosion protection is required. Zinc-plated washers per ISO 4042 are also available for indoor or less exposed applications.