Technical resources

Measure, identify, then review the requirement.

Practical references for maintenance, engineering and purchasing teams working from a drawing or a ring in hand.

These pages explain measurement methods and material families. Confirm the compound and application conditions before choosing a seal.

Measuring black and red O-rings with a caliper on a technical drawing
Measure the relaxed ring: inside diameter and cross section, in the original unit.

Method

Measure, identify, review

  1. OXXRING worksheet for recording ID, cross section and service notes 01 · MEASURERecord ID, CS and the original unit.Measure the relaxed ring without stretching it. The worksheet keeps inside diameter, cross section, original units and service notes together.Open the size and measurement guide
  2. Diagram identifying O-ring ID and cross section 02 · IDENTIFYUse the standard when the drawing gives one.AS568 dash numbers are inch based. Keep the recorded units when comparing a standard reference with measured ID × CS.Search AS568 sizes
  3. O-rings and seals in black, red, blue and grey compounds 03 · REVIEWCheck material against the service condition.Compare NBR, FKM, EPDM, Silicone and FFKM by temperature, media and typical use before narrowing the search.Compare material families

Next step

Ready to order? Start from the common sizes

Most equipment uses standard AS568 or metric sizes. Pick one to see every listed material and hardness, or search your exact ID × CS.

Buyer help

Common questions before you buy

Shipping, returns and payment details live in the store policies; the full buying FAQ is on the FAQ page.

Prepare a request
How do I find a size?

Use inside diameter (ID), cross section (CS), and the original measurement unit. Add the material and hardness when known. Find O-rings

When will my order ship?

Standard orders usually dispatch in 1–2 business days. Custom parts: with an existing mould usually 3–7 days; with a new mould, tooling and production take 13 days standard or as fast as 7 days rush. Dates are confirmed on the quote; shipping time is additional. Delivery after dispatch depends on the destination and service. Shipping details

Where can I check delivery terms?

Shipping destinations, current rates, delivery estimates and handling notes are maintained in our Shipping Policy. Delivery information

Can I request a custom size or documents?

Send the size, material, hardness, quantity and service conditions with your request. Include any required documents so they can be reviewed with the quotation. Prepare a request

Engineering answers

Questions about materials, service and seal design

Use these answers to identify the operating inputs and choose your next check.

O-Ring Material Selection Guide

Practical guidance for material selection, using operating conditions rather than one-size-fits-all rules.

How do I choose the right O-ring material?

Start with the fluid or chemical, temperature, motion, pressure and gland conditions. A material family can be a useful starting point, but the exact compound and application conditions still need validation.

Do not present family-level guidance as final compound approval.

Enter the operating medium and conditions to screen candidate material families.

Can I use the same O-ring material for static and dynamic sealing?

Not automatically. Dynamic seals add friction, wear, lubrication, speed and surface-finish requirements that can change the best material or compound choice even when chemical compatibility looks acceptable.

Chemical compatibility alone is not dynamic-service approval.

Provide speed or cycle rate, lubrication, surface condition and gland geometry for dynamic review.

Why does operating temperature matter when choosing an O-ring?

Temperature changes elastomer stiffness, compression behavior, fluid interaction and usable service margin. A temperature range for one compound or test condition should not be treated as a universal limit for every compound in the same material family.

Do not convert family or test temperatures into universal continuous-service limits.

Add normal and peak operating temperature to the material review.

Why can two compounds from the same elastomer family behave differently?

Compounds within the same elastomer family can use different formulations, hardness levels and additives. That is why a family-level compatibility rating can disagree with a specific compound test and why exact compound review matters for critical service.

Do not average conflicting family-level and compound-level evidence.

Use family screening first, then validate the exact compound for the application.

How much O-ring swelling is acceptable?

There is no single percentage that is safe for every application. Dynamic seals are usually more sensitive to swelling because friction, wear and toughness can change, while static seals may tolerate more depending on gland fill and assembly conditions.

Keep service guidance separate from qualification-test limits.

Review swelling together with motion, gland fill and the exact compound test context.

Compare materials

O-Ring Pressure, Gland & Backup Ring Guide

Practical guidance for pressure and gland design, using operating conditions rather than one-size-fits-all rules.

If a material is chemically compatible, is it automatically suitable for high pressure?

No. Chemical compatibility does not establish pressure capability. High-pressure sealing also depends on extrusion clearance, hardness, gland geometry, pressure direction and whether a backup ring is needed.

Never infer a pressure rating from compatibility evidence.

Provide pressure, clearance, hardness and gland details for extrusion review.

When does an O-ring need a backup ring?

Backup-ring need is driven by the combination of pressure, extrusion clearance, O-ring hardness, temperature and pressure direction. The correct number and location of backup rings also depends on whether pressure is one-way or can reverse.

Do not use a single pressure threshold as a universal rule.

Submit pressure direction, clearance and hardness for a backup-ring check.

Is a smoother sealing surface always better?

No. Dynamic seals need a surface that is smooth enough to limit wear but still able to retain a lubricating film. An extremely polished surface can reduce lubricant retention and increase friction in some dynamic applications.

Surface-finish units and metrics must not be converted without a verified method.

Include surface finish and lubrication condition in dynamic seal review.

Open engineering tools

O-Ring Vacuum & Gas Sealing Guide

Practical guidance for vacuum and gas sealing, using operating conditions rather than one-size-fits-all rules.

What changes when an O-ring is used in vacuum or gas service?

Vacuum and gas sealing add permeability, surface leakage and outgassing concerns that are less important in many liquid applications. Squeeze, surface condition, compound permeability and lubrication can all change leak behavior.

Do not turn reference leak calculations into pass/fail approval.

Provide gas or vacuum conditions, temperature, seal type and cleanliness requirements.

What is explosive decompression in an O-ring?

Gas can dissolve into an elastomer under pressure and then expand during rapid depressurization, creating blisters, pits, fissures or rupture. Risk depends on gas, pressure, compound, cross section, temperature, soak time and decompression rate.

Do not use one pressure threshold as a universal safe limit.

Provide gas type, maximum pressure and depressurization profile for review.

Review gas or vacuum service

O-Ring Failure Diagnosis & RFQ Guide

Practical guidance for failure diagnosis and rfq, using operating conditions rather than one-size-fits-all rules.

Can O-ring damage be diagnosed from a photo alone?

A photo can help rank likely failure modes, but appearance alone is not enough to prove a single root cause. Pressure history, motion, temperature, media, lubrication, installation and gland condition are often needed to separate similar-looking failures.

Never present image-only diagnosis as a confirmed root cause.

Use the visible damage as a starting point and collect the service history before deciding the root cause.

What information should I provide for an O-ring material recommendation or RFQ?

At minimum, provide the sealing medium and whether the application is static or dynamic. Temperature, pressure, size, quantity and—when relevant—speed, lubrication, surface finish, extrusion clearance, hardness and gland details make the review much more reliable.

RFQ readiness does not equal service approval, stock confirmation or lead-time commitment.

Submit the operating conditions, size and quantity for engineering review and quotation.

Review visible damage

Send operating conditions for review

Engineering reference

Rules of thumb and checks for a reliable seal

The design rules and checks we use when reviewing a size, material or groove. They are starting points: confirm them against your actual pressure, temperature, fluid and motion.

01

Standards and materials

AS568
The inch-based standard (current revision AS568F) that defines O-ring inside diameter, cross-section, tolerances and dash numbers. The dimensions apply to any elastomer that can be moulded to them, and include straight-thread tube-fitting boss gaskets (the -9xx dash numbers). AS568 size chart
Compound, not just material
An O-ring compound is a base elastomer plus curing agents, fillers and plasticizers. The recipe changes heat, chemical and wear behaviour, so two NBR or two FKM compounds can perform differently. Compare the data for the exact compound against your application.
02

Gland design rules of thumb

For static and reciprocating (non-rotating) O-rings in oil, hydraulic fluid or other normal lubricants, with controlled machining tolerances.

Gland fill
Keep the O-ring cross-section at or below about 90% of the groove's cross-section area, leaving room for heat expansion and fluid swell. Above 100% the ring has nowhere to go: redesign the groove rather than force the fit.
Installed stretch
Keep stretch to about 3% when the ring is stretched into its groove. If the nearest standard size needs more, a different or custom size is usually better than overstretching.
Extrusion gap
The clearance a seal can bridge depends on system pressure and O-ring hardness. If the gap is too large for the pressure, tighten the tolerance, choose a harder compound or add a backup ring.
Face seals
Seat the ring against the groove wall on the side away from the pressure: the outer wall when pressure is inside, the inner wall when it is outside. Pressure then cannot push the ring across the groove.
When these rules don't apply
High pressure, wide tolerances, very low friction targets or other fluids need the seal and groove design confirmed by test or engineering analysis.
03

Check before production

Review each point for the actual installation and service conditions.

  • Gland geometryGroove depth, width and fill for this installation
  • Compression setSqueeze the ring won't recover after long periods under load; depends on compound, temperature and time
  • Extrusion and nibblingAt high pressure; consider a backup ring
  • Chemical compatibilityWith every fluid, cleaner and lubricant the seal touches
  • Service temperatureNormal and peak
  • AbrasionIn moving (dynamic) applications
  • Surface finishOf the sealing faces and the groove
  • Lubrication and frictionAt assembly and in service
  • SwellingFrom chemical exposure; recheck gland fill
  • HardnessAgainst pressure, extrusion gap and service conditions

Then test the chosen compound and seal design in the real installation before production use.

04

Silicone in harsh environments: what tests show

Findings from published tests on specific silicone compounds. They show what to check, not ratings for silicone in general.

UV and atomic oxygen
In tests on three silicone compounds for a spacecraft docking seal, atomic oxygen raised leakage modestly; atomic oxygen plus UV raised it by up to 600 times and reduced seal adhesion. If a silicone seal will see UV, plasma or space-like conditions, test the exact compound.
Outgassing
The compounds in that study measured below 1.0% total mass loss and below 0.1% collected volatile condensable material (ASTM E595). For vacuum, optics or semiconductor equipment, ask for E595 data on the exact compound: it is not a property of silicone in general.
Dust and debris
In tests with a lunar-dust simulant, debris on silicone face seals greatly increased leakage unless the seal was fully closed; cleaning the seal generally brought leakage back to the as-new level. Keep sealing faces clean at assembly and protect face seals from grit.