Ready Plastics

Thermoset Tube — Standard Sizes, Wall Thicknesses & Stocking Guide

Thermoset tube is stocked in filament-wound and roll-wrapped form from 1/4″ bore to 12″+ OD across G10, phenolic-glass, and phenolic grades — knowing the standard sizing conventions prevents spec errors and speeds procurement.

TL;DR — Key Takeaways

  • Thermoset tube is specified by OD × wall thickness, or ID × OD, depending on manufacturer convention — always confirm both dimensions
  • Standard wall thicknesses: 1/16″, 3/32″, 1/8″, 3/16″, 1/4″, 3/8″, 1/2″ — heavier walls (1/2″+) are frequently special order
  • G10 and phenolic-glass tube are the most common grades for electrical insulation; phenolic tube is used for mechanical/structural applications
  • Filament-wound tube (hoop-wound) is the most common form for electrical applications; roll-wrapped sheet tube is used for structural shapes
  • Standard lengths are 36″ or 48″; cut-to-length service available

Thermoset Tube — Standard Dimension Table

Note: Not all OD × wall combinations are stocked at all distributors. Call for current stock availability before specifying.

Dimensional Conventions — OD vs ID Specification

Thermoset tube can be specified in two ways, and confusion between them causes common ordering errors:

OD-Specified Tube (Most Common)

The tube is defined by its outside diameter and wall thickness:

  • ID = OD − (2 × wall)
  • Example: 2.000″ OD × 0.125″ wall → ID = 2.000 − (2 × 0.125) = 1.750″

This is the most common stocking convention. The OD is the controlled dimension; the ID is derived.

ID-Specified Tube (Bore-Critical Applications)

For applications where the bore must fit a shaft or core (coil forms, motor windings, transformer cores):

  • Tube is specified by ID and wall
  • OD = ID + (2 × wall)
  • Example: 1.500″ ID × 0.125″ wall → OD = 1.500 + 0.250 = 1.750″

Always confirm with your supplier which convention the stocking dimensions use.

Manufacturing Methods — Filament Winding vs Roll-Wrapping

Filament-Wound Tube

Filament winding lays glass fiber rovings at controlled angles (typically 55–75° helical) onto a mandrel, impregnated with resin, and cured. The result is:

  • High hoop strength (resists internal pressure and radial collapse)
  • Good ID control — the mandrel defines the bore
  • Available in G10 (glass-epoxy) and phenolic-glass systems

Best for: High-voltage tube insulators, transformer spacers, motor bore liners, coil forms requiring precise ID.

Roll-Wrapped Tube

Roll-wrapped tube is made by winding prepreg (resin-impregnated fabric) sheets around a mandrel. The layup is predominantly axial (0°) with some circumferential wraps.

Best for: Structural tubes, mechanical bushings, tubes requiring controlled wall thickness and post-machining of OD.

Pull-Wound and Braided Tube

Some phenolic-glass and GPO-3 tubes are pull-wound (parallel to axis) or braided. These are less common in the standard catalog but available for custom geometry.

Tolerance Classes for Thermoset Tube

Per ASTM D709 and NEMA LI-1, tube tolerances depend on OD and whether the tube is filament-wound or roll-wrapped:

Grade-Specific Notes

G10 Tube

The preferred electrical insulation tube for high-voltage applications. Filament-wound G10 tube is the standard choice for:

  • Transformer winding spacers and bobbins
  • HV standoff tubes and bushings
  • Switchgear insulating supports

G10 tube is HB flammability — not V-0. When UL 94 V-0 is required, specify FR4 tube.

FR4 Tube

FR4 tube carries UL 94 V-0 in addition to G10's electrical properties. Less commonly stocked than G10 tube — confirm availability. For transformers and switchgear where V-0 is mandated (some UL and CSA standards), FR4 or GPO-3 tube is required.

Phenolic-Glass Tube (Phenolic-glass-silicone, G7)

G7 (glass-silicone) tube offers the highest continuous temperature rating (220°C) and is used in:

  • Aerospace and high-temperature motor windings
  • Transformer components near windings operating above 150°C
  • Radar and RF equipment requiring silicone matrix for low-loss properties

See the thermoset tubes for aerospace guide for aerospace-specific sizing and qualification.

Cotton-Phenolic Tube

Lower cost than glass-epoxy tube; adequate for mechanical applications (bushings, rollers) and low-voltage insulation. Limited electrical insulation capability vs G10 — use only for applications ≤ 600V dry service.

Ordering Checklist

When ordering thermoset tube, specify:

  1. Grade: G10, FR4, phenolic-glass, cotton-phenolic, etc.
  2. OD × Wall (or ID × Wall): Confirm convention with supplier
  3. Length: 36″ stock, 48″ stock, or cut-to-length
  4. Quantity: Pieces or linear feet
  5. Specification reference: ASTM D709, MIL-I-24768, NEMA grade
  6. Special requirements: Certified test report, C of C, halogen-free

Request thermoset tube pricing and availability

Request a Quote →

More related guides

Materials

Applications