industrial, machinery and appliance spare parts / Buying guide
Seals, gaskets and rubber parts
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The most expensive mistake in this category is commissioning a copy of something that has a standard designation. O-rings, oil seals, circlips and most bearings are made to international standards, and the equivalent is a catalogue lookup rather than a manufacturing project.
Measure before you commission. It takes ten minutes and it frequently ends the job.
In this guide
Identify before you commission
- O-rings: inner diameter and cross-section identify a standard size. Two measurements and you have a part number.
- Oil seals: inner diameter, outer diameter and width, usually moulded onto the seal itself along with the type.
- Gaskets: if it is a flange gasket, the flange standard defines it.
- Belts: length, width and profile are printed on most and measurable on all.
- Only after all of that comes a custom mould.
Material matters more than shape
- NBR — general purpose, oil resistant, poor with heat and ozone. The default and often the wrong one.
- FKM / fluoroelastomer — high temperature and chemical resistance, several times the price.
- EPDM — water, steam and weathering; incompatible with mineral oils.
- Silicone — wide temperature range, poor abrasion resistance.
- PTFE — chemically inert, used where nothing else survives.
- Getting the polymer wrong produces a part that fits perfectly and fails in weeks.
When a custom mould is the answer
When the profile is genuinely non-standard, or the original is obsolete and no equivalent exists. A simple compression mould runs into the low thousands of renminbi and produces hundreds of parts, so it makes sense at quantity and not at one.
For single pieces of a non-standard seal, machining from PTFE or polyurethane stock is usually faster and cheaper than tooling, at some cost in properties.
Questions & answers
Common questions
- Can you match a seal from a sample?
- Yes. Send it — dimensions and a hardness reading identify most seals, and the material can be inferred from the application or tested.
- What hardness should I specify?
- Match the original if you have it; a durometer reading on the old part settles it. Guessing wrong on hardness leaks as surely as guessing wrong on size.
- How long does a custom mould take?
- Two to three weeks for the mould and a sample, then production. Standard parts ship in days.
Your next step
Have a link you want checked?
Send a 1688 or Taobao product link and you get back the specification in English, the supplier check, and the landed cost to your country before you commit to anything.
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