Delrin Rod — Sizes, Tolerances & Ordering (POM-H Acetal)
Delrin rod is the highest-volume acetal homopolymer stock shape, used as lathe stock for CNC-turned precision parts — gears, bushings, valve bodies, spacers, and fasteners. Standard diameters run from 0.125" through 12.0" in natural (white/ivory) and black; 4-foot lengths are standard. Delrin 150 is the dominant extrusion grade for stock-shape rod due to its surface quality and dimensional stability after machining.
At a glance:
- Diameter range: 0.125" through 12.0" in standard increments
- Standard lengths: 4 ft (48"); some sizes in 6 ft
- Grades stocked: Delrin 150 (standard), 500, 150SA/500SA (FDA), 100AF (PTFE-filled), black
- Tolerances: ±0.010–0.030" OD depending on diameter (ASTM D6100)
- Centerline porosity: known characteristic of POM-H above ~3" dia; see note below
- Primary keyword: "delrin rod" — US volume 500/month, CPC $0.40
What Is Delrin Rod Used For?
Delrin rod is lathe stock. Engineers and machinists specify it when a part:
- Has a circular cross-section (turned parts, discs, plugs, stems)
- Requires tight OD tolerance as the starting dimension for turning to final size
- Benefits from Delrin's self-lubricating surface in the finished part (bushings, bearings)
- Needs a natural (white) or black appearance in the finished part
Common turned parts from Delrin rod include: gear blanks (then hobbed or molded), bushing blanks, valve seats, threaded standoffs, knobs, spacers, coupling bodies, cam followers, and lock cylinders.
Stocked Delrin Rod Diameters
| Diameter | OD Tolerance (ASTM D6100) | Standard Length | Grade Options |
|---|---|---|---|
| 0.125" (1/8") | ±0.010" | 4 ft | 150 natural, 500 natural |
| 0.187" (3/16") | ±0.010" | 4 ft | 150 natural, 500 natural |
| 0.250" (1/4") | ±0.010" | 4 ft | 150/500 natural/black |
| 0.312" (5/16") | ±0.010" | 4 ft | 150 natural |
| 0.375" (3/8") | ±0.010" | 4 ft | 150/500 natural/black |
| 0.500" (1/2") | ±0.010" | 4 ft | 150/500 natural/black; 150SA |
| 0.625" (5/8") | ±0.010" | 4 ft | 150/500 natural/black |
| 0.750" (3/4") | ±0.010" | 4 ft | 150/500 natural/black; 150SA |
| 1.000" (1") | ±0.010" | 4 ft | 150/500 natural/black; 150SA; 100AF |
| 1.250" | ±0.015" | 4 ft | 150/500 natural |
| 1.500" | ±0.015" | 4 ft | 150/500 natural/black; 150SA |
| 2.000" | ±0.015" | 4 ft | 150/500 natural/black |
| 2.500" | ±0.020" | 4 ft | 150 natural |
| 3.000" | ±0.020" | 4 ft | 150 natural |
| 4.000" | ±0.020" | 4 ft | 150 natural |
| 5.000" | ±0.030" | 4 ft | 150 natural |
| 6.000" | ±0.030" | 4 ft | 150 natural |
| 8.000" | ±0.030" | 4 ft | 150 natural |
| 10.000" | ±1% dia | 4 ft | 150 natural |
| 12.000" | ±1% dia | 4 ft | 150 natural |
Cut-to-length is available on most diameters. Minimum cut length typically 6 inches; call out cut tolerance when ordering.
Centerline Porosity in Delrin Rod
Delrin (acetal homopolymer, POM-H) develops a porous centerline zone in extruded rod diameters above approximately 3.0 inches. This is a characteristic of all POM-H homopolymer — not a manufacturing defect — and is accepted under ASTM D6100. The porosity results from volumetric shrinkage as the rod solidifies inward from the outer surface.
Impact on machining: parts where through-bores or features are centered on the rod axis (and therefore intersect the porous core zone) may show: (a) a rough or grainy inner bore surface, (b) reduced gas-tightness at the bore, (c) potential structural weakness in the core region.
If centerline-porosity-free material is required in diameters above 3", specify acetal copolymer (POM-C) rod instead. POM-C rod does not develop this characteristic. See acetal copolymer rod.
Grade Selection for Delrin Rod
Delrin 150 — Best choice for most machined parts from rod. Medium-high MW, optimized for extrusion; clean chips, excellent surface finish, best dimensional stability of the standard grades.
Delrin 500 — Marginally lower cost than 150; suitable when extrusion quality of 150 is not specifically needed. Also widely used in injection molding pellets (same grade).
Delrin 150SA — FDA-compliant version of Delrin 150, meeting 21 CFR 177.2480. Natural color only. For food-contact machined parts (wear strips, valve seats, conveyor components).
Delrin 500SA — FDA-compliant version of Delrin 500. Natural color.
Delrin 100AF — PTFE/aramid fiber filled. Black color. For high-duty bearing and bushing applications where standard Delrin exceeds its PV limit. Not FDA-compliant.
Black Delrin 150/500 — Carbon-black pigmented; not ESD-dissipative; not typically FDA-compliant. For applications where color contrast or cosmetics matter.
For the full grade decision tree, see Delrin grades.
How Delrin Rod Is Manufactured
Delrin rod is produced by extrusion: Delrin pellets are melted and forced through a circular die, then pulled through a water-cooled sizing mandrel that controls the OD tolerance. The extrusion process creates a radial crystallinity gradient in large-diameter rod — the surface cools and crystallizes faster than the core — which is the fundamental cause of centerline porosity in large sizes.
Smaller-diameter rod (< 2") solidifies more uniformly and does not develop significant porosity. This is why the centerline porosity concern is specific to large diameters.
Ordering and Cut-to-Length
Standard full-length rods ship as 4-foot (48-inch) lengths. Cut-to-length is available to within ±0.125" of the specified cut length for standard service; precision sawing to ±0.060" available on request.
Minimum order quantities and lead times vary by diameter and grade. Standard sizes (up to 4") typically ship from stock. Large diameters (>6") may require lead time; verify availability when ordering.
When specifying Delrin rod on a purchase order:
Delrin 150 rod (or Delrin 150SA if FDA-compliant), [diameter]" nominal OD, ASTM D6100, natural color, 4-foot lengths (or cut to [X]" ± 0.125"). Certificate of conformance required.
Machining Delrin Rod
Delrin rod turns cleanly on CNC lathes with standard carbide tooling at 400–800 SFM surface speed. For complete parameters — including drilling, tapping, threading, and finishing — see the Delrin machining guide.
Key rod-specific machining notes:
- For OD turning with significant material removal, leave 0.020–0.030" of finish stock and take a final light pass for best diameter tolerance
- For through-bores: drill to 0.010" undersize; ream or bore to final tolerance
- Chuck grip: soft jaws recommended for thin-wall sections; standard three-jaw for solid blanks
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