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Washers · Trade series (cup finishing washer) · Application guide

What Are Cup Finishing Washers Used For?

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

Cup Finishing Washers are used for seating a countersunk head on material too thin to countersink, or on timber and composite that would be weakened by one. They are manufactured to Trade series (cup finishing washer), and selection is driven by the nominal bolt size, the fit and tolerance the assembly requires, and the service environment.

Primary duty
Seating a countersunk head on material too thin to countersink, or on timber and composite that would be weakened by one
Governing standard
Trade series (cup finishing washer)
Nominal bolt size range
M6 to No.10 / M5
Category
Washers

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

What Are Cup Finishing Washers Used For? application image

Cup Finishing Washers are selected when an assembly calls for seating a countersunk head on material too thin to countersink, or on timber and composite that would be weakened by one. This application guide to the Trade series (cup finishing washer) type covers concrete end-uses, the specification checklist, correct installation, and where an alternative fastener performs better. Stocked across roughly M6 to M10, they cover general to heavy-duty work.

Typical Applications for Cup Finishing Washers

The most common settings where these are specified:

  • Maintenance & repair (MRO): a stocked size for servicing existing plant where the original fastener spec must be matched.
  • 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.

How to Specify Cup Finishing Washers for Your Application

  • Size: Match the nominal size to the mating thread or hole. This product spans M6–M10; 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 (cup finishing washer). 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 Cup Finishing 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 Cup Finishing 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 (Trade series (cup finishing washer))

For screw sizeInner diameter d1 (mm)Outer diameter d2 (mm)Overall height (mm)Sheet thickness (mm)MaterialFinishTypical use
No.6 / M3.54.011.03.00.6Stainless A2PolishedTrim, panelling
No.8 / M44.612.73.50.6Stainless A2PolishedTrim, panelling
No.10 / M55.414.34.00.7Stainless A2PolishedCabinetry
M66.517.54.50.8SteelNickelCabinetry
M88.522.05.00.9SteelNickelFurniture
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

Which industries use Cup Finishing Washers?

They are commonly specified in bolted structural joints, vibration applications and timber & soft materials, among other sectors.

How do I choose the right size of Cup Finishing Washers?

Match the nominal size to the mating thread or hole. This product is available from M6 to M10; the full dimension table on this page lists each size.

Do Cup Finishing 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 Cup Finishing 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.

Can I get a quote for Cup Finishing 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.