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

PTFE USIT Rings (Self-Centring Bonded Seals)

Temperature range, chemical and fluid compatibility, hardness and the full dimensional range for this compound.

PTFE USIT Rings (Self-Centring Bonded Seals) are supplied to polytetrafluoroethylene (thermoplastic, not an elastomer). Corrosion behaviour is near-universal chemical resistance; no elastic recovery, so it is used as a back-up or energised seal, the material is non-magnetic, and the usable service range is approx. -200 °C to +260 °C. In practice this grade is chosen for chemical service and low friction rather than for elastic sealing.

Grade: polytetrafluoroethylene (thermoplastic, not an elastomer)
Corrosion resistance: Near-universal chemical resistance; no elastic recovery, so it is used as a back-up or energised seal
Magnetic response: Non-magnetic
Service temperature: approx. -200 °C to +260 °C

Property values are typical for the grade. Certified mechanical test data is available on request for production orders.

USIT Rings (Self-Centring Bonded Seals) manufactured in PTFE (polytetrafluoroethylene (thermoplastic, not an elastomer)) are dimensioned to Trade series (self-centring bonded washers, USIT type). The sections below give the mechanical and physical properties of the grade, its behavior in corrosive and elevated-temperature service, and the full size table.

Why Choose PTFE for USIT Rings (Self-Centring Bonded Seals)

Chosen for chemical service and low friction rather than for elastic sealing. For usit rings (self-centring bonded seals), this matters when near-universal chemical resistance; no elastic recovery, so it is used as a back-up or energised seal is the primary requirement.

Mechanical & Physical Properties

Grade designation	polytetrafluoroethylene (thermoplastic, not an elastomer)
Magnetic response	Non-magnetic
Service temperature	approx. -200 °C to +260 °C
Corrosion characteristic	Near-universal chemical resistance; no elastic recovery, so it is used as a back-up or energised seal

Corrosion Behavior in Service

Carbon and alloy steel usit rings (self-centring bonded seals) require a coating for corrosion protection. Zinc plating (with or without passivation) is the most common; hot-dip galvanizing is used for outdoor structural service; black-oxide is mainly a tarnish-prevention finish for tool-room use.

Comparable Grades

For usit rings (self-centring bonded seals), consider an energised or spring-loaded PTFE seal where recovery is required, or FKM where the chemistry allows an elastomer. Elastomer selection is decided by the medium, the temperature range and whether the seal is static or dynamic — not by strength.

Sizes of USIT Rings (Self-Centring Bonded Seals) Available in PTFE

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

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

Item / category Standard Size(s) Material / finish Quantity

Business Information

Company * Contact Name * Email * Phone (with country code) Country / Region

Notes

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

Applications & Industries

USIT Rings are bought for a small number of well-defined jobs. These are the ones we ship them for. Stocked from M6 to M27.

Industries that specify USIT Rings

Machine tools Coolant and hydraulic ports.
Hydraulics Port plugs and fittings.
Mobile plant Vibration-prone joints.
Compressors Sealing under pressure cycling.
Process & food equipment Sealing at joints that are cleaned and inspected.
Hydraulics & pneumatics Static and dynamic sealing in cylinders and valve bodies.

Typical applications

seating the ring square before tightening
choosing the self-centring form where the seat is imperfect
matching the thread size exactly
selecting FKM where the fluid or temperature demands it
excluding dust and moisture from a housing
sealing a joint against fluid or air pressure

Service conditions to specify against

Sealed joints: Used where the fixing has to keep water or air out as well as hold — the elastomer, not the fastener, decides service life.

Where to use something else

Do not reuse a bonded or USIT seal after it has been compressed; the elastomer has taken a set and will not seal a second time.

Full application guide: where USIT Rings are used, how to specify them, and the cases they are wrong for

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.

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.
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.
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.
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

Can PTFE replace stainless steel structurally?

No — stainless A2/A4 cannot match class 10.9 / 12.9 strength. Stainless is selected for corrosion, not raw strength.

Are PTFE USIT Rings (Self-Centring Bonded Seals) magnetic?

PTFE USIT Rings (Self-Centring Bonded Seals) are non-magnetic.

What corrosion resistance do PTFE USIT Rings (Self-Centring Bonded Seals) offer?

PTFE USIT Rings (Self-Centring Bonded Seals) provide near-universal chemical resistance; no elastic recovery, so it is used as a back-up or energised seal with a service range of approx. -200 °C to +260 °C.

When should I move from polytetrafluoroethylene (thermoplastic, not an elastomer) to class 8.8 for USIT Rings (Self-Centring Bonded Seals)?

Step up to class 8.8 when the joint preload approaches the proof load of the current class. The higher class adds preload at the same diameter, often saving size and weight.

How do I request a quotation?

Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day.