---
title: "What Are Extra-Thick Flat Washers Used For?"
description: "Extra-Thick Flat Washers (Trade series (heavy-duty thick plain washers)) are used for load distribution and anti-loosening under a bolt or nut."
url: https://engineeringhardware.com/applications/extra-thick-flat-washers/
source: Engineering Hardware & Fasteners
---

# What Are Extra-Thick Flat Washers Used For?

Washers · Trade series (heavy-duty thick plain washers) · Application guide

Typical applications, the industries that specify extra-thick flat washers, and how to choose the right size, material and finish for the joint.

Extra-Thick Flat Washers are used for load distribution and anti-loosening under a bolt or nut. They are manufactured to Trade series (heavy-duty thick plain washers), and selection is driven by the nominal bolt size, the fit and tolerance the assembly requires, and the service environment.

- **Primary duty:** Load distribution and anti-loosening under a bolt or nut
- **Governing standard:** Trade series (heavy-duty thick plain washers)
- **Nominal bolt size range:** M10 to M20
- **Category:** Washers

Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation.

![What Are Extra-Thick Flat Washers Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/09/Extra-Thick-Heavy-Duty-Flat-Washers.webp)

Extra-Thick Flat Washers are used primarily for load distribution and anti-loosening under a bolt or nut. This page lists the industries and assemblies where they are specified, the selection criteria that matter for each application, installation practice, and the cases where a different fastener type is the correct choice. Parts are supplied to Trade series (heavy-duty thick plain washers). Stocked across roughly M10 to M20, they cover general to heavy-duty work.

## Typical Applications for Extra-Thick Flat Washers

The most common settings where these are specified:

- **Bolted structural joints:** spreading load over soft or oversized holes and protecting the surface.
- **Vibration applications:** spring and serrated types that maintain tension under cyclic load.
- **Timber & soft materials:** large-OD types that prevent pull-through.
- **General machine building:** fastening covers, brackets, motors and sub-assemblies on production equipment.
- **Maintenance & repair (MRO):** a stocked size for servicing existing plant where the original fastener spec must be matched.

Product catalog

## Related Extra-Thick Flat Washers products

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Flat & Other Precision Washers

### [Annealed Soft Material Compatibility Flat Stainless Steel Washer](https://engineeringhardware.com/product/annealed-soft-material-compatibility-flat-stainless-steel-washer/)

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### [Nta855 Nt855 Cummins Plain Washer 3041493 Seal Ring Genuine Diesel Engine Parts for Construction Machinery](https://engineeringhardware.com/product/nta855-nt855-cummins-plain-washer-3041493-seal-ring-genuine-diesel-engine-parts-for/)

Plain Washer · Metal

**US$6.00 – 12.00**MOQ 1 piece

[![Factory Manufactured Stainless Steel Metal Screw Washer D9021](https://img.engineeringhardware.com/Factory-Manufactured-Stainless-Steel-Metal-Screw-Washer-D9021.webp)](https://engineeringhardware.com/product/factory-manufactured-stainless-steel-metal-screw-washer-d9021/)

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### [Factory Manufactured Stainless Steel Metal Screw Washer D9021](https://engineeringhardware.com/product/factory-manufactured-stainless-steel-metal-screw-washer-d9021/)

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**US$0.0012 – 0.11**MOQ 200 pieces

[![Compact Car Camping Garden Washer with Brush Nozzles and 5 Bar Pressure](https://img.engineeringhardware.com/Compact-Car-Camping-Garden-Washer-with-Brush-Nozzles-and-5-Bar-Pressure.webp)](https://engineeringhardware.com/product/compact-car-camping-garden-washer-with-brush-nozzles-and-5-bar-pressure/)

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### [Compact Car Camping Garden Washer with Brush Nozzles and 5 Bar Pressure](https://engineeringhardware.com/product/compact-car-camping-garden-washer-with-brush-nozzles-and-5-bar-pressure/)

Plastic · CE, RoHS, CB

**US$39.64 – 45.55**MOQ 1 piece

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### [High Pressure Air Cleaner and Ultrasonic Vibration Cleaner/Killing Washer](https://engineeringhardware.com/product/high-pressure-air-cleaner-and-ultrasonic-vibration-cleaner-killing-washer/)

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**US$420.00**MOQ 1 set

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Flat & Other Precision Washers

### [Precision Customized DIN Standard H59 M8 M10 Cooper Brass Round Metal Flat Washer for Heavy Industry Hardware Fastener](https://engineeringhardware.com/product/precision-customized-din-standard-h59-m8-m10-cooper-brass-round-metal-flat-washer/)

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**US$0.036 – 0.36**MOQ 10,000 pieces

[View all Flat & Other Precision Washers →](https://engineeringhardware.com/fastener-products/washers/flat-other-precision-washers/) [Full product catalog](https://engineeringhardware.com/products/)

## How to Specify Extra-Thick Flat Washers for Your Application

- **Size:** Match the nominal size to the mating thread or hole. This product spans M10–M20; check the full table below for the exact dimensions of each size.
- **Type & OD:** Select flat for load spreading, spring/serrated for anti-loosening, or fender/large-OD for soft or oversized holes.
- **Environment:** For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient.
- **Standard:** This product is supplied to Trade series (heavy-duty thick plain washers). Quoting the standard on your order guarantees interchangeable dimensions between suppliers.

## Installation & Assembly Practice

- Place the washer under the rotating element (usually the nut) so tightening does not score the surface.
- Chamfered-hole side of a hardened washer faces the bolt head fillet.
- On serrated-flange hardware, do not add a plain washer — it defeats the serrations.

## Common Selection Mistakes with Extra-Thick Flat Washers

- Relying on a spring washer for locking on class 8.8+ joints — at high preload it flattens and adds nothing.
- Choosing an OD too small for soft material, so the head pulls through or embeds.

## Where Extra-Thick Flat Washers Are Not the Right Choice

A washer does not replace a locking feature on its own in severe vibration, and a spring washer adds little clamp on high-strength joints.

Custom manufacturing · Made to drawing

## Need a extra-thick flat washers outside the standard range?

Bearing area is usually the reason for a special washer: a larger outside diameter to spread load into a softer material, or a thicker section to resist dishing. Made by stamping or punching.

Minimum order from 2,000 pieces; samples within 7 days of drawing approval.

[Custom washer manufacturing](https://engineeringhardware.com/custom/washers/)[Send a drawing](https://engineeringhardware.com/custom/washers/#rfq)

## Technical Drawing

Dimensioned line drawing of M10 Extra-Thick Flat Washers to Trade series (heavy-duty thick plain washers). Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.

- **Material:** carbon steel or stainless steel
- **Relative thickness:** greater than the standard plain washer
- **Purpose:** reduce local deformation under heavy clamping
- **Finish options:** zinc plated or plain

## Dimensions & Specifications (Trade series (heavy-duty thick plain washers))

| Bolt size | Material | Relative thickness | Purpose | Finish options |
| --- | --- | --- | --- | --- |
| M10 | carbon steel or stainless steel | greater than the standard plain washer | reduce local deformation under heavy clamping | zinc plated or plain |
| M12 | carbon steel or stainless steel | greater than the standard plain washer | reduce local deformation under heavy clamping | zinc plated or plain |
| M16 | carbon steel or stainless steel | greater than the standard plain washer | increase bearing area on soft members | zinc plated or plain |
| M20 | carbon steel or stainless steel | greater than the standard plain washer | increase bearing area on soft members | zinc plated or plain |

Inside the plant

## Manufactured in our own plant

This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.

1. ![Wire rod feeding into a cold heading machine](https://engineeringhardware.com/wp-content/uploads/2026/08/09-wire-rod-feed-cold-heading-machine.webp) 01 **Cold heading** Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail. Head dimensions and under-head radius checked at set-up and per shift.
2. ![Thread rolling machine producing bolt threads](https://engineeringhardware.com/wp-content/uploads/2026/08/03-thread-rolling-machine-bolt-production.webp) 02 **Thread rolling** Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch. Go / no-go ring gauges to ISO 965 tolerance class 6g.
3. ![Baskets of bolts staged for heat treatment](https://engineeringhardware.com/wp-content/uploads/2026/08/05-heat-treatment-baskets-black-bolts.webp) 03 **Heat treatment** Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it. Core hardness and tensile tested per lot to ISO 898-1.
4. ![Zinc plated bolts in a treatment basket](https://engineeringhardware.com/wp-content/uploads/2026/08/23-zinc-plated-bolts-treatment-basket.webp) 04 **Surface treatment** Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list. Coating thickness and neutral salt spray hours to ISO 9227.

## Frequently Asked Questions

### Do Extra-Thick Flat Washers actually stop bolts loosening?

Spring and serrated washers help maintain tension under light vibration, but for critical joints a prevailing-torque locking nut or adhesive is more reliable. Flat washers mainly spread load and protect the surface.

### What material should Extra-Thick Flat Washers be for outdoor use?

For damp, coastal or chemical environments specify A4 (316) stainless or a suitably coated steel. For indoor or dry use, A2 (304) stainless or zinc-plated steel is normally adequate.

### Are Extra-Thick Flat Washers made to a recognized standard?

Yes — they are manufactured to Trade series (heavy-duty thick plain washers), so dimensions are interchangeable between suppliers when you quote the standard on your order.

### What are Extra-Thick Flat Washers used for?

Load distribution and anti-loosening under a bolt or nut. They are supplied to Trade series (heavy-duty thick plain washers).

### Can I get a quote for Extra-Thick Flat Washers in the size and material I need?

Yes. Use the technical drawing and quote form on this page to set the size and options, then send the exact configuration to our team for pricing and lead time.

## Related Pages

Product page: [Extra-Thick Flat Washers — specifications & sizes](https://engineeringhardware.com/fastener/extra-thick-flat-washers/)

### Extra-Thick Flat Washers Specification Guides

### Related Fastener Applications