Plastic Rod Stock: Diameters, Materials & Specifications
Plastic rod stock is cylindrical bar supplied in diameters from 1/8" to 12" and cut-to-length pieces typically 2, 4, or 6 feet long. It is the primary form for turning shafts, bushings, bearings, gears, pump components, and any round machined part. Most engineering plastics are available in rod; material selection drives whether extruded or cast production is appropriate, which in turn determines dimensional tolerance, residual stress, and the presence or absence of centerline porosity.
TL;DR
- Diameter range: 1/8" (0.125") to 12", material-dependent
- Extruded rod: best for diameters up to ~4"; tighter OD tolerance, may have center stress
- Cast rod: preferred for large-diameter Nylon; lower residual stress but potential centerline voids above 4–6" dia
- Key materials: Acetal, Nylon 6/6, PEEK, UHMW-PE, PEI (Ultem), PVDF (Kynar), PTFE, cotton phenolic, phenolic paper
- Stress-relieved rod recommended for close-tolerance turning applications
- Standard length: 2 ft (most diameters); 4 and 6 ft available for smaller diameters
- OD tolerance typically ±0.010"–±0.030" on extruded; ±0.030"–±0.060" on cast
Size Table — Plastic Rod Diameters by Material
| Material | Min Dia | Max Dia | Process | Std Lengths | Notes |
|---|---|---|---|---|---|
| Acetal (Delrin) | 1/8" | 6" | Extruded | 2 ft, 4 ft | Natural & black |
| Nylon 6/6 | 1/4" | 6" | Extruded | 2 ft, 4 ft | Lower moisture uptake |
| Nylon 6 | 1/2" | 12" | Cast | 2 ft | Better for large dia |
| PEEK | 1/4" | 6" | Extruded | 2 ft | Natural; 30%GF available |
| UHMW-PE | 1/2" | 8" | Extruded/Ram | 2 ft | Natural, black, FDA blue |
| PEI (Ultem) | 1/4" | 4" | Extruded | 2 ft | Amber; 1010/2010 grades |
| PVDF (Kynar) | 1/4" | 4" | Extruded | 2 ft | Natural; high-purity grades |
| PTFE | 1/4" | 12" | Molded/Ram | 2 ft | Pure & filled (GF, Bronze) |
| Cotton phenolic | 1/2" | 6" | Molded | 2 ft | NEMA LE; lathe-turnable |
| Phenolic paper | 1/2" | 4" | Molded | 2 ft | NEMA XX; electrical grade |
| PPS (Ryton) | 1/4" | 3" | Extruded | 2 ft | 40%GF standard |
| Polypropylene | 1/2" | 6" | Extruded | 2 ft | Natural & black |
| HDPE | 1/2" | 8" | Extruded | 2 ft | FDA grades available |
| ABS | 1/4" | 4" | Extruded | 4 ft | Natural & black |
Materials Available in Rod
Acetal Rod
Acetal rod is among the most popular plastic rods for its machinability, dimensional stability, and low friction. Moisture absorption stays below 0.25%, so turned parts hold tight tolerances even in humid environments. Natural Acetal is FDA-compliant; black is standard for industrial components. Tensile strength: 9,500–10,000 psi; hardness: Rockwell M90.
Nylon Rod
Nylon rod comes in extruded Nylon 6/6 (to 6" dia, tighter tolerance, ~3.5% moisture equilibrium) and cast Nylon 6 (to 12" dia, more isotropic, ~6.5% moisture equilibrium). MoS₂-filled Nylon adds dry-running lubricity for sleeve bearings. All Nylon rod must be dimensioned for moisture swell: absorbed moisture causes ~0.006"–0.010" growth per inch of diameter.
PEEK Rod
PEEK rod handles continuous service to 480°F (250°C). Extruded in natural and 30% glass-filled grades; carbon-fiber and PTFE-filled grades available on order. Tensile strength: 14,500 psi unfilled; up to 24,000 psi glass-filled. Used for semiconductor wafer-handling arms, medical sterilization parts, and aerospace fastener bodies.
UHMW-PE Rod
UHMW-PE rod delivers the best abrasion resistance of any commodity thermoplastic combined with near-zero moisture absorption. It is ram-extruded rather than screw-extruded due to its extremely high molecular weight, which prevents conventional melt processing. Standard diameters to 8"; FDA-compliant natural and blue grades are stocked. Common applications: wear bushings, chain guide pins, star wheels, and slow-speed bearing journals.
PVDF Rod
PVDF (Kynar) rod is specified for semiconductor wet-bench fittings, fluid-handling components, and chemical pump bodies. Natural PVDF rod is UL94 V-0 rated and has a continuous service temperature of 275°F (135°C). PVDF is one of the few fluoropolymers that can be machined on conventional CNC equipment without special tooling. Extruded in diameters from 1/4" to 4".
PTFE Rod
PTFE rod is compression-molded from powder (sintered), producing a dense, void-free bar resistant to virtually all chemicals. The coefficient of friction (0.05–0.10 dynamic against steel) makes PTFE rod the first choice for low-friction sliding components, seals, and valve seats. Available from 1/4" to 12" diameter in pure PTFE, 15% glass-filled (improved wear), 25% carbon-filled (best wear life and thermal conductivity), and bronze-filled (highest compressive load capacity).
Phenolic Rod
Cotton phenolic rod (NEMA LE grade) and phenolic paper rod (NEMA XX) are precision-turned from compression-molded cylinders. They offer excellent machinability, high compressive strength (~35,000–40,000 psi), and stable electrical insulation properties up to 250°F. Used for electrical standoffs, bearing cages, and gear blanks where cost is a consideration.
PEI, PPS, and Other Engineering Grades
PEI (Ultem) rod provides a UL94 V-0 flame rating and 340°F continuous use temperature in a machinable, amorphous form. PPS (Ryton) rod in 40% glass-filled grade offers near-zero moisture absorption and chemical resistance approaching PTFE in many media. Both are available in standard diameter increments and ship within 1–5 business days for stock sizes.
How Plastic Rod Is Made
Extrusion
Most rod under 4" diameter is screw-extruded: pellets melt through a circular die, pulled over a haul-off conveyor, and cooled in a vacuum-sizing sleeve that sets final diameter. Extruded rod carries residual stress from the surface-to-core cooling differential; specify stress-relieved rod for tight-tolerance turning.
Ram Extrusion
UHMW-PE is ram-extruded because its molecular weight prevents melt processing. A hydraulic ram pushes compacted powder through a heated die, producing rod with consistent cross-section properties.
Compression Molding and Sintering
PTFE rod is compression-molded from powder and sintered at ~700°F, yielding a void-free, fully dense bar. Phenolic rod is compression-molded from resin-impregnated fiber, producing a thermoset that cannot be re-melted.
Cast Rod
Cast Nylon 6 is produced by anionic polymerization of liquid caprolactam in cylindrical molds — the only practical route for large diameters (4"–12"). The result is more isotropic than extruded Nylon, but centerline porosity is a known issue above ~4–6" diameter.
Specifications & Tolerances
OD Tolerance
| Process | Diameter Range | Typical OD Tolerance |
|---|---|---|
| Extruded (most eng. plastics) | 1/8"–2" | ±0.010"–±0.020" |
| Extruded (most eng. plastics) | 2"–4" | ±0.020"–±0.030" |
| Ram-extruded (UHMW) | 1/2"–8" | ±0.030"–±0.060" |
| Cast Nylon 6 | 1/2"–6" | ±0.030"–±0.050" |
| Cast Nylon 6 | 6"–12" | ±0.050"–±0.100" |
| Compression-molded PTFE | 1/4"–12" | ±0.020"–±0.060" |
Centerline Porosity in Cast Rod
Centerline voids occur in cast Nylon rod above approximately 4–6" diameter because the core cools more slowly than the outer surface, causing volumetric shrinkage toward the center. When machining large-diameter cast Nylon to a finished bore, inspect the centerline area for porosity. For critical applications, specify "porosity-free certified" or use extruded Nylon where the geometry allows.
Stress Relief
Extruded rod carries residual stresses that relax during machining, causing warpage or size change. Request stress-relieved (annealed) rod for bore tolerances tighter than ±0.002", wall sections under 0.250", or critical flatness requirements. Typical anneal temperatures: Acetal 220–250°F, Nylon 250–300°F, PEEK 450–480°F, at 1–4 hours per inch of diameter.
Cutting & Finishing
Cutoff Sawing
Rod is parted on a horizontal band saw or cold saw. Use M2 HSS blades (10–14 TPI) for most thermoplastics; carbide for glass-filled or phenolic grades. Secure the rod firmly — round stock is prone to rolling during cutoff. A work stop ensures perpendicular faces.
Turning and Boring
Plastic rod turns easily on CNC lathes with positive-rake carbide or polished HSS tooling. Sharp tools are critical — dull cutters generate heat that melts and gums thermoplastics. Flood coolant (water-soluble) is standard; compressed air works for Acetal, PEEK, and Nylon. Typical surface finish: 32–63 µin Ra on finishing passes. For precision bores, use a single-point boring bar rather than a drill — drills deflect and produce tapered, oversized holes in soft plastics. Ream for H7 or better fits.
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