Material
Delrin (Acetal) Parts
The engineering plastic that machines like a dream.
Delrin, generically acetal or POM, is the first material to reach for when a part should be plastic: slippery against metal without lubrication, stiff and stable for a polymer, nearly zero water absorption, and it machines into accurate parts as readily as brass. Bushings, gears, guides, wear pads, and fixtures are its home turf. Send a STEP and print through the quote form; quotes come back in 24-48 hours.
Updated June 2026
Delrin / Acetal
Stiff, slippery, and dimensionally stable. The default plastic for bushings, guides, and wear parts.
Typical parts
- Bushings & rollers
- Guide blocks
- Insulating spacers
- Low-friction wear parts
Delrin, acetal, POM: same family, one real choice
All three names point at the same plastic. POM is the polymer, acetal is the generic term, and Delrin is DuPont’s brand of the homopolymer version. The practical split is homopolymer versus copolymer: homopolymer (Delrin) is a little stronger and stiffer; copolymer resists hot water and chemicals better and avoids the low-density centerline that homopolymer rod can carry. Most parts are happy in either. If your spec names Delrin specifically, or the part lives in hot water, say so in the quote notes and the right stock gets quoted.
What gets made from it
Wear and motion parts, mostly: bushings and sleeve bearings, rollers, slides and guides, gears that need to run quietly without grease, cam followers, and wear pads that keep steel from rubbing steel. Acetal is naturally slippery against metal, doesn’t swell or corrode, and won’t chew up the more expensive part it runs against.
The other half of the work is lab and instrument components, insulators, seal seats, test fixtures, and food-machinery parts, where a stable, easy-to-clean plastic that holds dimension is the whole requirement. Most of it is turned or milled in small batches, with no minimum order.
Acetal or nylon?
Dimensional stability is the dividing line. Nylon absorbs a few percent of its weight in water and grows as it does, so a nylon part that fit in January can bind in August. Acetal absorbs almost nothing and holds the size it was cut to. Nylon hits back with better abrasion resistance, more toughness, and a lower price.
The rule of thumb: if the part has a fit, a bore, or a tolerance that matters, acetal. If it’s a sacrificial wear block or a sheave that just needs to be tough and cheap, nylon does fine. Both quote normally.
Tolerance honesty for plastic parts
Plastic moves more than metal, and it’s better to design for that than to fight it. Acetal’s thermal expansion is roughly ten times steel’s, so a fit dimensioned at 68 °F behaves differently in a hot enclosure. ±0.005 in is comfortable on acetal parts; ±0.001-0.002 in is achievable on critical features when the print calls for it, though it’s worth asking whether the assembly actually needs metal-grade numbers at temperature.
Two design notes that save revisions: give plastic fits a little more clearance than the metal version would get, and call out which dimensions are critical so inspection focuses where it counts.
Questions
Before you send a job.
01 Is Delrin the same thing as acetal?
Delrin is DuPont’s brand name for homopolymer acetal; “acetal” unqualified usually means the copolymer. Homopolymer is slightly stronger and stiffer, copolymer handles hot water and aggressive cleaning better, and rod-form homopolymer can carry a less-dense centerline that matters on thin-walled turned parts. If your drawing says Delrin and means it, note that; otherwise the better-suited one gets quoted.
02 Is Delrin food-safe?
FDA-compliant grades of both homopolymer and copolymer acetal exist and are common in food machinery. The certification belongs to the specific stock, not the material family, so flag food contact in the quote notes and the parts get cut from certified material with the paperwork to match. Natural (white) is the usual call for food service.
03 What tolerances can acetal parts hold?
±0.005 in is routine, and ±0.001-0.002 in is achievable on critical diameters and bores when the print demands it. The honest caveat is that plastic moves with temperature and humidity more than metal does, so a tolerance that tight is only useful if the fit is controlled at the temperature the part lives at. Tolerance the critical features and let the rest breathe.
04 Should this part be acetal or nylon?
Acetal when dimensions matter: it barely absorbs water, so bores and fits stay where they were cut. Nylon when the job is abrasion and impact on a budget and a little swelling is harmless. Wet environments tip the scale hard toward acetal. Describe the application in the quote notes and the material question gets settled before pricing.
05 When should I step up from Delrin to PEEK?
When the environment outruns acetal: continuous service much above 180 °F, steam or autoclave cycles, or chemicals that attack acetal. PEEK survives all three and costs many times more, so it’s a requirements decision, not an upgrade. If the part lives at room temperature in air or water, acetal is almost always the better buy.
Related
Where to go next.
PEEK
For the heat, steam, and chemistry acetal can’t take.
View →CNC Turning
Where bushings and rollers get quoted.
View →Medical & Lab
Instrument parts in stable, cleanable plastics.
View →Custom Bushings
Quiet, self-lubricating sleeve bushings.
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