POM properties
Polyoxymethylene, also called acetal or polyacetal. It's a semi-crystalline engineering thermoplastic: stiff, low in friction, and of the common machinable polymers it absorbs the least moisture.
- TypesPOM-C copolymer and POM-H homopolymer. Delrin is a DuPont trade name for POM-H
- Density1.41 g/cm³, about half the weight of aluminium
- TensileAround 62–65 MPa for POM-C, around 70 MPa for POM-H
- ServiceRoughly 90–100 °C continuous. Melting point is 165–175 °C, and it does not soften gradually on the way there
- MoistureAround 0.2 % uptake, which is why POM holds size and nylon does not
- ExpansionAround 110 × 10⁻⁶ per K, roughly nine times steel and five times aluminium
- FrictionLow and self-lubricating. Gears, bushings, slides and wear strips are its natural use
- ChemicalsGood against fuels, solvents and neutral chemicals. Attacked by strong acids and by chlorine in water
- BondingGlue won't hold on it without surface treatment. Design for screws, snaps or press fits
- CertificateBatch traceability and the material supplier's own data sheet and compliance declarations on request
A plastic tolerance without a temperature is not a tolerance. A 200 mm POM part grows about 0.11 mm for every 5 °C. We inspect in a climate-controlled room at 20 °C and report on that basis. If your incoming inspection is done on a warm bench you'll get different numbers, and both sets can be correct. That's why the drawing should state the measuring temperature.
POM compared with related plastics
| Material | Common trade names | US (ASTM) | ISO | Typical form here | Cross-reference |
|---|---|---|---|---|---|
| POM-C copolymer, our default | Hostaform · Ultraform · Tecaform | ASTM D6100 class 2 | ISO 9988 | Rod and sheet, natural and black | Direct equivalent |
| POM-H homopolymer | Delrin (DuPont trade name) | ASTM D6100 class 1 | ISO 9988 | Rod, natural and black | Not a drop-in |
| POM-C + PTFE low friction | Tecaform AH LA and similar | No single ASTM class | No single ISO class | Rod, grey-brown | Not a drop-in |
| PA6 cast MC Nylon, the usual alternative | MC901 · Nylatron | ASTM D4066 | ISO 1874 | Rod and sheet | Not a drop-in |
We list trade names because plastics get specified by brand much more often than metals do. A drawing that only says "Delrin" names a product, not a standard. Let us know whether you need POM-H specifically or any acetal, since that changes what we buy and what it costs. Last reviewed 13 September 2026.
Copolymer, homopolymer, or something else
POM-C for machined parts, almost always
Copolymer is the default for machining from stock. It stands up better to hot water and alkalis, it's easier to get in rod and sheet, and it does not have the centreline problem described below. This is what we quote unless the drawing gives a reason for something else.
The centreline porosity problem in POM-H
Extruded homopolymer rod above roughly 50 mm diameter can have a band of low-density material running down its axis. If the part is machined from that zone, you can end up with a porous or voided surface that looks like a manufacturing defect even though it's in the stock. When a drawing calls for POM-H in a thick section, we raise this before quoting.
POM-C with PTFE where friction is the requirement
Bushings, slides and wear strips running dry. It costs more and has slightly lower mechanical properties, so we'd only specify it where the friction figure really matters.
Not for hot water or strong acid
POM breaks down in continuous hot water, in chlorinated water and in strong acids. Parts for those conditions are usually made in PVDF, PTFE or PEEK. It's better to settle that before the drawing is released.
Not where nylon is specified for a reason
MC Nylon is tougher and handles impact better. It also takes on up to several percent moisture and swells as it does, and that's the reason POM gets picked for parts that must hold size. On a dimensioned drawing you cannot swap one for the other.
Not outdoors unless it's black
Natural POM chalks and turns brittle under UV, while carbon-black grades hold up much better. If the part will live outside, specify black on the drawing as a material requirement. A cosmetic colour note is not enough.
Machining process
POM cuts very well. Most of the effort goes into holding a soft part without distorting it, keeping heat down, and giving the part time to settle before we measure it.
- TurningMori Seiki and Okuma lathes to Ø 310 × 800 mm. With a sharp, honed edge POM turns to a mirror finish
- MillingDoosan, Haas, Hision and FANUC RoboDrill machining centres, 3, 4 and 5-axis
- ToolingSharp high-rake tooling, polished flutes, single or two flute. A dull edge melts the surface rather than cutting it
- CoolingAir blast or a light mist, with chips cleared all the time. Chips left in the cut melt onto the part
- FixturingLight clamping and support underneath. Clamping pressure that would not mark aluminium will deform POM
- RelaxationRough, rest, then finish. Machined stock releases internal stress and keeps moving for hours afterwards
- AnnealingAvailable where a tight-tolerance part must be dimensionally settled before inspection
- InspectionMitutoyo CRYSTA-APEX V CMM in a climate-controlled lab at 20 °C, reported in inch and millimetre
We quote plastic tolerances wider than metal ones for physical reasons: expansion, deflection under clamping and stress relaxation. On small features and short dimensions we can sometimes go tighter than the figures above. Send the drawing and we'll answer for your part specifically. General tolerance follows ISO 2768 medium class unless your print says otherwise.
Compatible and incompatible finishing processes
- As machinedTurned and milled surfaces come off clean and glossy. Most parts need no secondary finishing
- MarkingLaser marking on black and dark grades. Contrast on natural white is poor
- AnnealingStress relief for dimensional stability on tight-tolerance parts, before final inspection
- DeburringHand deburr as standard. POM burrs are soft and easy to miss on an inspection bench
- Not forPainting, plating and printing. Nothing adheres to POM without surface treatment
- Not forSolvent bonding. Design for screws, press fits or snap features instead of glue
Colour is decided when the material is bought. POM comes as natural white or black stock, and we can't colour it after machining. If the part has to be black for UV or for looks, put that on the drawing so it's priced into the material and not found out at packing. Full finishing list →
Stock and lead time
- POM-C rodNatural and black, common diameters, available from Vietnamese stockists
- POM-C sheetCommon thicknesses available; large sheet confirmed per job
- POM-HAvailable, ordered in more often than POM-C. We check the section size against the centreline issue before buying
- Filled gradesPTFE-filled and glass-filled grades ordered in per job
- QuoteWithin 24 business hours of a complete RFQ
- Lead timePrototype 3–7 days · small batch 7–14 days · standard 14 days after PO
- DocumentsBatch traceability plus the resin maker's data sheet and compliance declarations, on request
Plastics do not come with an EN 10204 3.1 mill certificate the way steel does. We can give you batch traceability to the supplier and the material producer's own declarations, including food-contact statements where the grade has them. Those declarations come from the material supplier. We pass them on as issued and do not restate them as our own. Our ISO 9001:2015 certificate scope names aluminium, steel and stainless steel. Plastic parts go through the same inspection and documentation route, but they're outside that scope.
Common questions
Is Delrin the same as POM?
Delrin is DuPont's trade name for POM-H, the homopolymer. POM-C is the copolymer, sold under names such as Hostaform and Ultraform. Both are acetal. The differences show up in thick sections and in hot water.
Which should I specify, POM-C or POM-H?
POM-C for almost all machined parts. It's easier to source and handles hot water and alkalis better. It also does not have the centreline density problem that large diameter extruded POM-H rod can have.
What tolerance can you hold on a plastic part?
Routinely ±0.02 mm, and ±0.01 mm on small features, measured at 20 °C. The machine is not the limit here. POM expands about nine times as much as steel for the same temperature change.
Why did my part measure differently when it arrived?
Almost always temperature. A 200 mm POM dimension moves roughly 0.11 mm per 5 °C. We inspect at 20 °C in a climate-controlled room, so a bench at 30 °C will read differently. Put the measuring temperature on the drawing.
Can POM parts be glued?
Not reliably, and not without surface treatment. Design for screws, press fits or snap features. If the assembly relies on bonding, it's worth reconsidering the material before the drawing is released.
Do you have food-grade POM?
Food-contact grades exist and we can source them. We supply the material producer's own compliance declaration for that batch, as issued.
Can you machine PEEK, PTFE or nylon as well?
Yes. PEEK, PTFE, MC Nylon, PA, PC, ABS and HDPE all run here. Each behaves differently under the cutter and holds different tolerances, so send the drawing with the material named and we'll quote that part specifically.
Related information
6061-T6 aluminium
The metal alternative when a plastic part cannot hold size or temperature.
304 stainless steel
Where a wear or hygiene part has to survive cleaning chemicals and heat that POM will not.
Finishing and heat treatment
Every finish and heat treatment condition we offer, and what we check before shipping.