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Washers · BS 4518 · Application guide

What Are Bonded Sealing Washers Used For?

Typical applications, the industries that specify bonded sealing washers, and how to choose the right size, material and finish for the joint.

Bonded Sealing Washers are used for load distribution and anti-loosening under a bolt or nut. They are manufactured to BS 4518, and selection is driven by the thread 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
BS 4518
Thread size range
M4 to M36
Category
Washers

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

What Are Bonded Sealing Washers Used For? application image

Bonded Sealing 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 BS 4518. Stocked across roughly M4 to M36, they cover general to heavy-duty work.

Typical Applications for Bonded Sealing Washers

The most common settings where these are specified:

  • Fabrication & metalwork: bench and on-site assembly of steel frames, enclosures and weldments.
  • 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.

How to Specify Bonded Sealing Washers for Your Application

  • Size: Match the nominal size to the mating thread or hole. This product spans M4–M36; 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 BS 4518. 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 Bonded Sealing 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 Bonded Sealing 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.

Technical Drawing

Customize the parameters below — every spec field is editable, and the drawing redraws to match the values you choose. Changing the size will snap the other fields to that size's standard values; you can then override any individual value.

Sends the selected values to the quote form below.

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The form below follows the current technical drawing configuration. Change the drawing values above and the request details update automatically.

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Specification
Business Information

Dimensions & Specifications (BS 4518)

Thread sizeInner diameter d1 (mm)Outer diameter d2 (mm)Thickness s (mm)Seal materialMax temperature (deg C)Reference standard
M44.181.0NBR120BS 4518
M55.1101.0NBR120BS 4518
M66.1121.5NBR120BS 4518
M88.2141.5NBR120BS 4518
M1010.2161.5NBR120BS 4518
M1212.2192.0NBR120BS 4518
M1414.2212.0NBR120BS 4518
M1616.3242.0NBR120BS 4518
M1818.3262.0NBR120BS 4518
M2020.3282.0NBR120BS 4518
M2222.3302.0NBR120BS 4518
M2424.3322.0NBR120BS 4518
M2727.4362.5NBR120BS 4518
M3030.4392.5NBR120BS 4518
M3333.5432.5NBR120BS 4518
M3636.5462.5NBR120BS 4518

Video: What Are Bonded Sealing Washers Used For? in use

How do Bonded Seals Work?

Third-party video, selected automatically for this topic. It is not produced by Engineering Hardware and is not a specification source — use the tables on this page for dimensional data.

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
    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
    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
    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
    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

How do I choose the right size of Bonded Sealing Washers?

Match the nominal size to the mating thread or hole. This product is available from M4 to M36; the full dimension table on this page lists each size.

Do Bonded Sealing 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 Bonded Sealing 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 Bonded Sealing Washers made to a recognized standard?

Yes — they are manufactured to BS 4518, so dimensions are interchangeable between suppliers when you quote the standard on your order.

Can I get a quote for Bonded Sealing 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.