Flat / Plain Washer - Grade 202, 304, 316, A2, A2-70

A plain washer, or flat washer, is a basic and circular metal piece with a central hole. Its purpose is to evenly distribute the weight of a threaded fastener, such as a bolt or screw, across a larger surface. This ensures protection for the attached material and adds stability to the fastening.

Plain / Flat Washer Technical Specification

Attribute	Description
Shape	Round disc with concentric hole
Function	Load distribution, surface protection, spacing
Standards	DIN 125, ISO 7089, ASTM F844, BS4320
Common Sizes	M3 to M36 (metric); 1/8" to 1-1/2" (inch)
Materials	Mild steel, stainless steel (304, 316), brass, copper, aluminum, nylon
Finishes	Zinc-plated, hot-dip galvanized, black oxide, plain, passivated

Stainless Steel 316 is ideal for marine and corrosive environments.
Mild Steel is economical but rusts easily without plating.
Nylon washers are non-conductive and used for electrical insulation.
Brass & Copper washers offer good thermal and electrical conductivity.

Plain / Fat Washer – Material Comparison

Material	Temperature Resistance	Common Applications
Mild Steel	Up to ~250°C	General-purpose, indoor assemblies
Stainless Steel 304	Up to ~870°C	Food industry, outdoor, light corrosive environments
Stainless Steel 316	Up to ~870°C	Marine, chemical, pharmaceutical
Brass	Up to ~200°C	Plumbing, electrical, decorative uses
Copper	Up to ~200°C	Electrical grounding, heat conduction
Aluminum	Up to ~150–200°C	Lightweight assemblies, electronics
Nylon (Plastic)	Limited (~80–100°C)	Electrical insulation, non-load-bearing applications
Hot-Dip Galvanized Steel	Up to ~250°C	Outdoor/structural with enhanced rust protection

A plain washer, also known as a flat washer, is a thin, flat, circular metal disc with a central hole. It is used to distribute the load of a threaded fastener (like a bolt or screw) and prevent damage to the material surface.

Stainless Steel 304 / 316

Up to ~870°C

Key Composition / Standards

18% Cr, 8% Ni – A2-70 (metric)

Yield Strength (MPa)

1000 Max

Hardness (HB / HRC)

~300 HB / 32–35 HRC

Function

The main purpose of a plain washer is to expand the contact area of a fastener, minimizing strain on the material being attached. This is particularly crucial when dealing with delicate materials or when the fastener hole exceeds the size of the fastener head.

Material

Different materials can be used to manufacture plain washers, such as steel (carbon steel, stainless steel), aluminum, brass, and even plastic or rubber.

Applications

Plain washers have a wide range of uses in various industries and applications, such as general fastening, electrical work, automotive engineering, plumbing, and sheet metal work.

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