G7 Rod — Diameters, Lengths & Tolerances
G7 rod is round bar stock produced from NEMA G-7, a glass-fiber reinforced silicone resin thermoset laminate offering the highest continuous service temperature among the NEMA glass-reinforced grades at 220 °C (425 °F). Unlike the epoxy-based G11 and FR5 grades, G7 uses a silicone resin matrix that delivers outstanding arc resistance, superior performance under repeated thermal cycling, and reliable dielectric properties at extreme heat — making G7 rod the material of choice for machined insulators, arc barriers, and structural components in high-temperature electrical equipment, power transformers, and aerospace support systems.
At a glance:
- Diameter range: 0.250" to 4.0"
- Standard lengths: 4 ft and 8 ft
- OD tolerance: ±0.005" on smaller diameters; ±0.010" on larger diameters
- Material: NEMA G-7, glass-fabric/silicone thermoset laminate
- Production method: Compression-molded and ground to round
- Color: Natural off-white to light tan
Standard Diameter Table
G7 rod is stocked in the following standard sizes at Ready Plastics:
| Diameter | Standard Lengths | Notes |
|---|---|---|
| 0.250" | 4 ft & 8 ft | Small insulator and bushing blank |
| 0.375" | 4 ft & 8 ft | |
| 0.500" | 4 ft & 8 ft | |
| 0.750" | 4 ft & 8 ft | |
| 1.000" | 4 ft & 8 ft | Arc barrier and insulator blank |
| 1.500" | 4 ft & 8 ft | |
| 2.000" | 4 ft | |
| 3.000" | 4 ft | Heavy structural insulator blanks |
Custom diameters and cut lengths 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's silicone matrix delivers superior arc resistance and thermal stability compared to G11 and FR5, though tensile and flexural values are somewhat lower than epoxy-glass grades. Specify G7 when arc resistance or extreme-heat performance drives the material selection.
Typical Applications
G7 rod is machined into high-temperature and arc-resistant electrical components:
- Arc barriers and arc chutes in circuit breakers and disconnect switches — silicone resin resists carbonization from electrical arcing
- High-temperature insulators and standoffs in transformer and motor lead connections exposed to sustained 200+ °C ambient temperatures
- Bushing blanks for turbine generators and large rotating machines — maintains mechanical integrity through thermal cycling
- Structural support rods in industrial ovens and heat-treating equipment — 220 °C continuous rating covers most industrial process temperatures
- Insulating spacers and tie rods in high-voltage switchgear where arc tracking must be prevented
- Aerospace and defense fixture components requiring extreme temperature and dielectric performance
Machining G7 Rod
G7 rod machines on conventional CNC lathes and mills with carbide tooling. The silicone resin matrix is somewhat more abrasive than epoxy grades, so tool sharpness is important — replace inserts more frequently than you would for G10 or G11 to maintain surface finish quality. Use moderate cutting speeds with positive-rake carbide inserts; light air blast keeps the cutting zone clear. Dry machining is preferred; avoid water-based coolants on finished surfaces as they may temporarily elevate moisture at the surface. Drilled holes and tapped threads hold well — the material is not brittle under controlled machining conditions.
Related
- G7 Glass Silicone — Line Card
- G7 Sheet — flat stock for high-temp arc-resistant insulation panels
- G7 Tube — hollow sections for extreme-temperature sleeves and coil forms
- G11 Rod — high-temperature epoxy-glass rod for applications below 180 °C