G7 Tube — IDs, ODs, Wall Thicknesses & Lengths
G7 tube is hollow cylindrical stock produced from NEMA G-7, a glass-fabric/silicone thermoset composite offering continuous service to 220 °C (425 °F) — the most extreme continuous thermal rating in the standard NEMA glass-laminate family. The silicone resin matrix provides G7 tube with outstanding arc resistance, excellent thermal cycling stability, and reliable dielectric performance in extreme-heat environments. G7 tube is specified for coil forms in Class H and Class C transformers, insulating sleeves through high-temperature zones in industrial process equipment, arc-resistant conduit in switchgear, and structural spacer tubes in turbine and generator assemblies.
At a glance:
- Wall thickness range: 0.062" to 0.500"+ (ID/OD combinations vary)
- Standard lengths: 12" to 48" nominal; longer cuts available
- Wall tolerance: ±0.010" typical
- Material: NEMA G-7, glass-fabric/silicone thermoset
- Production method: Filament-wound or compression-molded tube
- Color: Natural off-white to light tan
Standard Tube Size Table
G7 tube is stocked in common ID/OD combinations at Ready Plastics:
| ID | OD | Wall | Standard Length | Notes |
|---|---|---|---|---|
| 0.500" | 0.750" | 0.125" | 24" & 48" | Insulating sleeve blank |
| 0.750" | 1.000" | 0.125" | 24" & 48" | |
| 1.000" | 1.375" | 0.187" | 24" & 48" | Coil form / bobbin |
| 1.250" | 1.625" | 0.187" | 24" & 48" | |
| 1.500" | 2.000" | 0.250" | 24" & 48" | Conduit and structural sleeve |
| 2.000" | 2.500" | 0.250" | 24" & 48" | |
| 2.500" | 3.000" | 0.250" | 24" | Larger bore insulating sleeve |
| 3.000" | 3.750" | 0.375" | 24" | Heavy structural spacer tube |
Custom ID/OD configurations and wall thicknesses are available on request.
Mechanical & Electrical Properties
| Property | Value |
|---|---|
| Tensile strength | 45,000 psi (310 MPa) |
| Flexural strength (LW, 0.125") | 25,000 psi (170 MPa) |
| Shear strength | 17,000 psi (115 MPa) |
| Bond strength | 900 psi (6.2 MPa) |
| Hardness (Rockwell M) | 105 |
| Izod impact strength (49 °C, LW) | 6.50 ft·lb/in |
| Specific gravity | 1.78 |
| Water absorption (24 hr) | 0.20% |
| Flammability rating | UL 94V-0 |
| Maximum continuous service temp | 220 °C (425 °F) |
Note: G7 delivers outstanding arc resistance and thermal stability. Where maximum mechanical strength is the primary driver and temperatures remain below 180 °C, G11 tube may be more appropriate.
Typical Applications
G7 tube serves as the hollow insulating component in the most thermally severe electrical and industrial environments:
- Transformer coil forms and bobbins in Class H (180 °C) and Class C (220 °C) systems — silicone resin tolerates high varnish impregnation cure temperatures
- Insulating sleeves in industrial furnace wiring assemblies — 220 °C continuous rating covers sustained process temperatures
- Arc-resistant conduit in switchgear and power distribution — silicone matrix prevents tracking carbonization across tube surfaces
- Structural spacer tubes in turbine generators and large rotating machines — maintains dimensional stability through thermal cycling
- High-voltage guide tubes and probe sleeves in test equipment operating at extreme temperatures
- Aerospace and defense insulation components requiring the arc resistance and thermal range of silicone-glass construction
Machining G7 Tube
G7 tube is machined using carbide tooling — the silicone-glass composite is moderately abrasive, so tool sharpness must be maintained to prevent surface tearing. For facing and OD/ID turning, use positive-rake carbide inserts at moderate surface speeds with light chip loads. Band saw and chop saw cutting with carbide blades produces clean square ends; fine-tooth blades minimize exit-face chipping. When drilling through the wall, back the tube with a solid plug to prevent breakout. Silica dust generated during machining requires dust collection and appropriate respiratory protection in accordance with local safety regulations. Bonding to G7 tube ends is achieved with structural epoxy or silicone-compatible adhesives.
Related
- G7 Glass Silicone — Line Card
- G7 Rod — solid round bar for arc barriers and high-temp machined insulators
- G7 Sheet — flat stock for arc barrier plates and extreme-temperature insulation panels
- G11 Tube — high-temperature epoxy-glass tube for 180 °C applications