---
title: "What Are USIT Rings (Self-Centring Bonded Seals) Used For?"
description: "USIT Rings (Self-Centring Bonded Seals) (Trade series (self-centring bonded washers, USIT type)) are used for containing fluid or excluding contamination at…"
url: https://engineeringhardware.com/applications/usit-rings/
source: Engineering Hardware & Fasteners
---

# What Are USIT Rings (Self-Centring Bonded Seals) Used For?

Seals · Trade series (self-centring bonded washers, USIT type) · Application guide

Typical applications, the industries that specify usit rings (self-centring bonded seals), and how to choose the right size, material and finish for the joint.

USIT Rings (Self-Centring Bonded Seals) are used for containing fluid or excluding contamination at a static or dynamic interface. They are manufactured to Trade series (self-centring bonded washers, USIT type), and selection is driven by the thread size, the fit and tolerance the assembly requires, and the service environment.

- **Primary duty:** Containing fluid or excluding contamination at a static or dynamic interface
- **Governing standard:** Trade series (self-centring bonded washers, USIT type)
- **Thread size range:** M6 to M27
- **Category:** Seals

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

![What Are USIT Rings (Self-Centring Bonded Seals) Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/09/USIT-Rings.webp)

USIT Rings (Self-Centring Bonded Seals) (Trade series (self-centring bonded washers, USIT type)) are specified where the joint requires containing fluid or excluding contamination at a static or dynamic interface. The sections below cover the typical end-uses by industry, the size and material decisions for each, assembly practice, and the applications this fastener type is not suited to. Stocked across roughly M6 to M27, they cover general to heavy-duty work.

## Typical Applications for USIT Rings (Self-Centring Bonded Seals)

The most common settings where these are specified:

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

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## How to Specify USIT Rings (Self-Centring Bonded Seals) for Your Application

- **Size:** Match the nominal size to the mating thread or hole. This product spans M6–M27; check the full table below for the exact dimensions of each size.
- **Material:** Choose the material and finish for the service environment — plated steel for general use, stainless for corrosion resistance.
- **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 (self-centring bonded washers, USIT type). Quoting the standard on your order guarantees interchangeable dimensions between suppliers.

## Where USIT Rings (Self-Centring Bonded Seals) Are Not the Right Choice

Match the fastener to the load, environment and whether the joint must be reopened; the wrong class or style is the usual cause of joint failure.

Custom manufacturing · Made to drawing

## Need a USIT rings (self-centring bonded seals) outside the standard range?

Inside diameter, cross-section and compound are the three that matter, and the compound is chosen against the fluid and the temperature rather than the dimensions.

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

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

## Technical Drawing

Dimensioned line drawing of M6 USIT Rings (Self-Centring Bonded Seals) to Trade series (self-centring bonded washers, USIT type). Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.

- **Seal element:** NBR inner lip
- **Metal carrier:** zinc-plated steel
- **Typical service:** hydraulic ports and plugs

## Dimensions & Specifications (Trade series (self-centring bonded washers, USIT type))

| Thread | Seal element | Metal carrier | Typical service |
| --- | --- | --- | --- |
| M6 | NBR inner lip | zinc-plated steel | hydraulic ports and plugs |
| M8 | NBR inner lip | zinc-plated steel | hydraulic ports and plugs |
| M10 | NBR inner lip | zinc-plated steel | hydraulic ports and plugs |
| M12 | NBR inner lip | zinc-plated steel | hydraulic ports and plugs |
| M14 | NBR or FKM inner lip | zinc-plated or stainless | hydraulic and fuel |
| M16 | NBR or FKM inner lip | zinc-plated or stainless | hydraulic and fuel |
| M18 | NBR or FKM inner lip | zinc-plated or stainless | hydraulic |
| M20 | NBR or FKM inner lip | zinc-plated or stainless | hydraulic |
| M22 | NBR inner lip | zinc-plated steel | hydraulic |
| M27 | NBR inner lip | zinc-plated steel | hydraulic |

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

### What are USIT Rings (Self-Centring Bonded Seals) used for?

Containing fluid or excluding contamination at a static or dynamic interface. They are supplied to Trade series (self-centring bonded washers, USIT type).

### Which industries use USIT Rings (Self-Centring Bonded Seals)?

They are commonly specified in general machine building, maintenance & repair (mro) and fabrication & metalwork, among other sectors.

### How do I choose the right size of USIT Rings (Self-Centring Bonded Seals)?

Match the nominal size to the mating thread or hole. This product is available from M6 to M27; the full dimension table on this page lists each size.

### Are USIT Rings (Self-Centring Bonded Seals) made to a recognized standard?

Yes — they are manufactured to Trade series (self-centring bonded washers, USIT type), so dimensions are interchangeable between suppliers when you quote the standard on your order.

### Can I get a quote for USIT Rings (Self-Centring Bonded Seals) 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: [USIT Rings (Self-Centring Bonded Seals) — specifications & sizes](https://engineeringhardware.com/fastener/usit-rings/)

### USIT Rings (Self-Centring Bonded Seals) Specification Guides

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