Short answer: Before PTFE gasket production, agree four tolerance questions with your supplier: thickness tolerance (the one that governs everything), ID/OD cut tolerance, squareness/concentricity for bolted gaskets, and — for compressed joint-style applications — overall flatness. Then agree the one question people forget: at what temperature these tolerances apply. Clear answers here eliminate most gasket rejects and re-quotes.
Gasket tolerances matter differently than machined-part tolerances: a gasket deforms in service by design. What you’re really specifying is consistency between batches, because that’s what your bolting procedure was validated against.
The Four Questions
- Thickness: ask for the band (±5% typical, ±0.05 mm achievable) and whether it’s measured at multiple points or one. Thin gaskets on high-load flanges deserve the tighter band.
- ID/OD: die-cut parts hold ±0.5 mm routinely; CNC-cut ±0.1 mm. Decide whether your assembly actually needs better than die-cut before paying for it.
- Bolt-hole positions: for gaskets with bolt holes, hole diameter and pitch-circle tolerance — mispositioned holes cause installation damage, the leading “manufacturing defect” that’s actually a tolerance agreement gap.
- Flatness: relevant for large-diameter or thick gaskets; warped gaskets create leak paths before any load is applied.
The Temperature Clause
| Specified at | Effect on a ±0.1 mm thickness band |
|---|---|
| 23 °C stated | Verifiable — both parties measure the same way |
| Not stated | Disputable — shop at 30 °C reads differently than QC at 18 °C |
One sentence in the PO — “thickness tolerances valid at 23 °C, measured per supplier’s documented method” — closes the argument before it opens.
Consistency Beats Perfection
For repeat gasket programs, batch-to-batch consistency on thickness matters more to your bolted-joint behavior than absolute precision. Ask how the supplier monitors thickness drift across batches — SPC records are the professional answer. Chunhuan certifies gasket thickness to ±0.05 mm with lot-level measurement records, tolerances referenced to a stated temperature.
Frequently Asked Questions
What gasket tolerances should be agreed before production?
Thickness band, ID/OD cut tolerance, bolt-hole position and pitch circle, and flatness for large sections — plus the temperature at which all of these apply.
What thickness tolerance can PTFE gaskets hold?
±5% of nominal is typical for die-cut; CNC production and skived stock reach ±0.05 mm with lot-level measurement records.
Why do bolt-hole tolerances matter on gaskets?
Mispositioned or undersized holes cause installation tearing — the most common ‘defect’ reported, usually traceable to an unspecified tolerance agreement.
Should gasket tolerance be exact or consistent?
For repeat programs, batch-to-batch consistency governs joint behavior more than absolute precision — ask for the supplier’s SPC on thickness drift.
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