PROFESSIONAL MANUFACTURER OF HARDWARE PRODUCTS
Jinan Meierde Industry Co., Ltd
Flat Washer
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Product introduction
Product Overview
Flat washers—also known as plain washers—are fundamental fastening components designed as thin, flat rings with a central hole. Unlike active fastening elements such as spring washers that store elastic energy, flat washers are passive components that serve critical load-distribution and surface-protection functions in bolted assemblies.
A washer is not loaded on tensile strength; therefore, it has a hardness specification instead of a tensile strength rating. The hardness indicates how easily the material deforms under compression. Flat washers are versatile components with applications ranging from spacing and pre-load indication to wear protection.
These components are essential across virtually every industry—including construction, automotive, machinery, aerospace, electronics, and precision assemblies—wherever threaded fasteners are used.
How Flat Washers Work
Flat washers perform several essential functions in a bolted joint:
Load distribution – The primary function of a flat washer is to evenly distribute the clamping force of a fastener over a larger bearing area, preventing the bolt head or nut from digging into the mating surface. This is especially critical when joining soft materials like aluminum, wood, or plastic.
Surface protection – By providing a hardened bearing surface between the fastener and the workpiece, flat washers protect painted, finished, or soft surfaces from damage during tightening.
Bridging oversized holes – Flat washers can span holes that are larger than the fastener head or nut, ensuring proper load transfer.
Spacing and adjustment – Washers can be used as shims to adjust the bearing area or take up axial play in assemblies.
Wear protection – In dynamic assemblies, flat washers provide a sacrificial surface that can be replaced when worn, protecting more expensive components.
Types of Flat Washers
By Dimensional Series
| Type | Description | Typical Applications |
|---|---|---|
| Type A | Standard flat washers with broad dimensional tolerances | General-purpose applications |
| Type B | Tighter dimensional tolerances; available in narrow, regular, and wide patterns | Precision assemblies requiring closer fits |
| SAE Pattern | Smaller outside diameter | Automotive and general engineering |
| USS Pattern | Larger outside diameter | Heavy-duty and structural applications |
By Form
| Form | Characteristics |
|---|---|
| Form A | Standard flat washer, no chamfer |
| Form B | Flat washer with chamfer on one edge |
| Form C | Flat washer with chamfer on both edges |
| Form G (Penny Washer) | Large outside diameter approximately 3× nominal thread diameter for maximum load distribution |
By Specialized Type
Narrow pattern – Dimensions smaller than SAE sizes
Regular pattern – Dimensions between SAE and USS sizes
Wide pattern – Dimensions larger than USS sizes
Fender washers – Extra-wide outside diameter for sheet metal and thin materials
Hardened structural washers – High-hardness washers for structural bolting applications
Technical Specifications
Dimensional Parameters
| Parameter | Description |
|---|---|
| Nominal Size | Compatible bolt/screw thread diameter (metric or imperial) |
| Inside Diameter (ID) | Clearance hole for the bolt shank |
| Outside Diameter (OD) | Overall outer dimension |
| Thickness (t) | Material thickness |
Example: M20 flat washer – ID 21mm, OD 37mm, Thickness 2.2mm
Dimensional Tolerances
Flat washers are manufactured with specific tolerances to ensure proper fit and function. Typical tolerances include:
| Dimension | Typical Tolerance |
|---|---|
| Inside Diameter | +0.5/-0 mm |
| Outside Diameter | +0/-0.8 mm |
| Thickness | +0/-0.4 mm |
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