Acetal Copolymer Rod — Sizes, Tolerances & Ordering (POM-C)
Acetal copolymer (POM-C) rod is the round stock form of Celcon, Hostaform, or equivalent acetal copolymer, used as lathe stock for CNC-turned precision components. In common industry usage, "acetal rod" without further qualification typically refers to acetal copolymer — the more widely stocked material. It differs from Delrin rod (acetal homopolymer, POM-H) in two important ways: no centerline porosity in large diameters, and better resistance to hot-water degradation.
At a glance:
- Primary keyword: "acetal rod" — US volume 150/month
- Diameter range: 0.125" through 8.0" standard; larger sizes available
- Standard length: 4 ft; cut-to-length available
- Key advantage over Delrin rod above 3" dia: no centerline porosity
- Grades: standard natural (white), black, FDA-compliant natural
- Tolerances: ±0.010–0.040" OD per ASTM D6100
"Acetal Rod" vs. "Delrin Rod" — Which Is Which?
In industrial distribution, "acetal rod" without further qualifier is supplied as acetal copolymer (POM-C) in most cases. Delrin is a DuPont trademark for acetal homopolymer (POM-H); when engineers specify "Delrin rod," they are requesting the specific POM-H product. When they specify "acetal rod" or "generic acetal rod," distributors typically supply POM-C.
This matters because they are different materials with different properties — particularly for hot-water service and large-diameter applications. If your application requires specifically POM-H (Delrin), specify it explicitly on the purchase order. See Delrin rod for POM-H-specific sizing.
Why Choose Acetal Copolymer Rod Over Delrin Rod?
For diameters above 3.0 inches: Acetal copolymer rod is uniform and pore-free throughout the cross-section. Delrin (POM-H) rod above ~3" develops a porous centerline zone during extrusion solidification — a known characteristic, not a defect, but one that affects parts requiring through-bores or gas-tight machined surfaces in the core region.
For hot-water or hydrolysis-sensitive applications: Parts machined from acetal copolymer rod and exposed to hot water (60–82°C) maintain their properties. Delrin rod in the same service degrades progressively.
For cost-sensitive general machined parts: POM-C rod is marginally less expensive than Delrin 150. For non-fatigue-critical applications, POM-C delivers equivalent performance at a slight cost advantage.
Stocked Acetal Copolymer Rod Diameters
| Diameter | OD Tolerance (ASTM D6100) | Standard Length | Color Options |
|---|---|---|---|
| 0.125" (1/8") | ±0.010" | 4 ft | Natural |
| 0.187" (3/16") | ±0.010" | 4 ft | Natural |
| 0.250" (1/4") | ±0.010" | 4 ft | Natural / black |
| 0.312" (5/16") | ±0.010" | 4 ft | Natural |
| 0.375" (3/8") | ±0.010" | 4 ft | Natural / black |
| 0.500" (1/2") | ±0.010" | 4 ft | Natural / black |
| 0.625" (5/8") | ±0.010" | 4 ft | Natural / black |
| 0.750" (3/4") | ±0.010" | 4 ft | Natural / black |
| 1.000" (1") | ±0.010" | 4 ft | Natural / black |
| 1.250" | ±0.015" | 4 ft | Natural |
| 1.500" | ±0.015" | 4 ft | Natural / black |
| 2.000" | ±0.015" | 4 ft | Natural / black |
| 2.500" | ±0.020" | 4 ft | Natural |
| 3.000" | ±0.020" | 4 ft | Natural |
| 4.000" | ±0.020" | 4 ft | Natural |
| 5.000" | ±0.030" | 4 ft | Natural |
| 6.000" | ±0.030" | 4 ft | Natural |
| 8.000" | ±0.040" | 4 ft | Natural |
Cut-to-length available for most diameters; standard cut tolerance ±0.125"; precision saw cut ±0.060".
Grade Options for Acetal Copolymer Rod
Standard natural (white): The default stocked grade — POM-C to ASTM D6100, natural color. Most standard natural Celcon and Hostaform grades meet FDA 21 CFR 177.2480 (verify with lot documentation). Used for general machined parts.
Black: Carbon-black pigmented POM-C. Cosmetic or contrast requirements. Not typically FDA-compliant.
FDA food-grade natural: Standard natural POM-C rod with FDA 21 CFR 177.2480 compliance letter supplied. Required for food-contact machined parts; specify "with FDA compliance documentation" on purchase order.
Lubricated (special order): Celcon M90-44 equivalent or Hostaform XAP2 equivalent; internally lubricated for bearing/sliding applications. Available in rod form to special order.
Dimensional Tolerances and Straightness
OD tolerances are tabulated above per ASTM D6100. Note: standard OD tolerances are asymmetric in practice — most suppliers hold the OD to the minus side to ensure the rod fits standard tooling and chucks.
Straightness: Standard rod is straight within 0.050"/ft. Precision-straightened rod to 0.010"/ft available for long-turning and precision bar-feed operations.
Surface condition: Extruded rod has a smooth but not polished surface. No skin or scale removal is needed before turning.
Applications for Acetal Copolymer Rod
The same applications as Delrin rod, plus the applications where POM-C's specific advantages matter:
- Hot-water system components: Machined from acetal copolymer rod for service in dishwashers, hot-water valves, and water treatment equipment
- Large flanges and discs (>3" dia): Where centerline porosity from POM-H would be unacceptable
- General-purpose CNC-turned parts: Spacers, plugs, coupling bodies, valve seats, threaded standoffs
- Bushings and bearing sleeves: Dry-running or lubricated service in mechanical assemblies
- Food-contact components: With FDA-compliant natural grade
Ordering Acetal Copolymer Rod
Specify on your purchase order:
Acetal copolymer (POM-C) rod, [diameter]" nominal OD, ASTM D6100 Type I, natural color. 4-foot lengths (or cut to [X]" ± 0.125"). Certificate of conformance required. [Add "FDA 21 CFR 177.2480 compliance documentation required" if food-contact grade needed.]
Avoid ordering "acetal rod" without specifying POM-C if the application specifically requires POM-C (e.g., for hot-water service or large-diameter parts without centerline porosity).
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