Ready Plastics

Thermoset Rod — Standard Sizes, Diameters & Stocking Guide

Thermoset rod is stocked in standard diameters from 1/4″ to 6″ across phenolic, glass-epoxy, and fabric-phenolic grades — understanding standard sizes prevents unnecessary oversizing, minimizes waste, and speeds quoting.

TL;DR — Key Takeaways

  • Standard thermoset rod diameters run 1/4″ through 6″ in fractional increments (1/4, 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 2, 2-1/2, 3, 4, 5, 6″)
  • Standard stock lengths are 36″ or 48″ per piece; some grades available in 60″ or 72″
  • Rod is sold at nominal diameter (or slightly oversize per ASTM D709) to allow finish machining
  • Phenolic rod (cotton-phenolic, linen-phenolic) is more widely stocked at smaller diameters; glass-epoxy (G10 and FR4) rod stocking thins above 3″
  • Custom diameters and long lengths are available on order lead times of 4–8 weeks for most grades

Standard Thermoset Rod Diameter Table

ASTM D709 Oversize Allowance for Rod

Per ASTM D709, thermoset rod is supplied at nominal diameter or slightly oversize (never undersize) to allow for finish machining to final OD:

A 1.000″ nominal rod may measure up to 1.010″ as-received — always confirm the as-received OD before designing a slip-fit component around nominal diameter alone.

Grade-Specific Stocking Notes

Cotton-Phenolic and Canvas-Phenolic Rod (C, CE, LE)

Cotton-phenolic is the most commonly stocked fabric-phenolic rod. Available in the full diameter range from 1/4″ to 6″+. Linen-phenolic (LE) is slightly less available above 3″.

Best-stocked sizes: 1/2″, 3/4″, 1″, 1-1/2″, 2″ in 36″ and 48″ lengths.

Key use: Machined gears, sprockets, bushings, silent chain guides, and structural electrical insulators.

G10 Rod (Glass-Epoxy, No FR)

G10 rod is the preferred choice for high-voltage insulators machined from solid round stock. Stocking availability is strong up to 3″; larger diameters are typically on order.

Best-stocked sizes: 1/2″, 3/4″, 1″, 1-1/4″, 1-1/2″, 2″ in 36″ lengths.

Key use: HV standoffs, transformer bushings, spacers for switchgear.

FR4 Rod (Glass-Epoxy, Flame-Retardant)

FR4 rod availability generally parallels G10. Specify FR4 when the application requires UL 94 V-0 or when MIL-I-24768/14 GEF is called out.

Important: FR4 and G10 are different materials. FR4 contains brominated flame retardants; G10 does not. Do not substitute G10 for FR4 when V-0 is specified.

Phenolic-Paper Rod (XX, XXX)

Paper-phenolic rod is less commonly stocked than fabric-phenolic because cotton-phenolic offers better machinability at similar cost. Available primarily in 1/2″ to 2″ diameters.

Key use: Low-cost insulators for dry indoor applications; terminal board dowels.

GPO-3 Rod

GPO-3 rod is less widely stocked than sheet but available in common sizes (1/2″, 1″, 1-1/2″, 2″). The random-fiber mat reinforcement means GPO-3 rod is not ideal for precision-machined cylindrical parts — prefer woven-glass G10 or FR4 for close-tolerance turning.

Custom and Non-Standard Diameters

When no standard size provides enough stock for your OD tolerance:

  1. Step up to next standard diameter and machine to finished size — preferred approach for precision parts
  2. Wound-to-order rod: For very large diameters (6″+), some laminators wind custom-diameter rod to order; lead times 8–16 weeks
  3. Machine from thick plate: For diameters up to 6″, round blanks can be profiled from thick thermoset sheet in cases where rod is unavailable

Length Options and Cutting

Standard stock lengths are 36″ or 48″. Custom cut-to-length service is typically available from distributors (±1/8″ saw cut tolerance). For precision-length cuts, specify a machined-end squareness tolerance.

Long lengths (72″, 96″) may be available for some phenolic grades by special order. Shipping long thermoset rod requires careful packaging — unsupported lengths over 48″ can bow during transit (see straightness tolerances).

How to Order Thermoset Rod

A complete rod specification call-out includes:

  1. NEMA grade (e.g., G10) or MIL type (e.g., GEE per MIL-I-24768/14)
  2. Nominal diameter (e.g., 1-1/2″)
  3. Length (e.g., 36″ or cut to 12.50″ ± 0.125″)
  4. Quantity (pieces)
  5. Any special requirements (certified test reports, C of C, QPL)

Example: "G10 per ASTM D709, 2.000″ diameter × 36″ long, 10 pieces, C of C required"

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