G7 Glass Silicone Laminate Specifications & Sizes
G7 phenolic glass silicone sheet, rod, and tube are governed by NEMA LI-1 for commercial supply and MIL-I-24768/17 for military procurement. Understanding the applicable specification, standard stock dimensions, and tolerance requirements before issuing a purchase order avoids procurement delays — G7 is not a commodity laminate, and non-standard dimensions typically require laminator lead times of four to ten weeks.
At a glance:
- Standards: NEMA LI-1 Grade G7; MIL-I-24768/17 Type GS
- Sheet stock: 0.031 in. to 4.0 in. thick; typical panel sizes 36×48 in. and 48×96 in.
- Rod: 0.25 in. to 6.0 in. diameter; 4-ft and 8-ft lengths
- Tube: wall from 0.062 in.; custom ID/OD programs standard
- Thickness tolerance: ±10% per NEMA LI-1 (tighter by agreement)
- Lead time: ex-stock for common thicknesses; custom laminations 4–10 weeks
Governing Standards
NEMA LI-1
NEMA LI-1, published by the National Electrical Manufacturers Association, is the primary commercial specification for laminated thermosetting insulating materials. It defines:
- Material grade designations (G7, G9, G10, FR4, etc.)
- Minimum property requirements per grade (flexural, dielectric, arc resistance, water absorption)
- Test method references (ASTM D-149, D-790, D-495, D-570, etc.)
- Dimensional tolerances for sheet, rod, and tube
All commercial G7 sheet sold in the United States is nominally produced to NEMA LI-1 unless otherwise specified. The standard does not require third-party certification or lot-level testing.
MIL-I-24768/17
MIL-I-24768 is maintained by the Defense Logistics Agency (DLA). Sheet /17 covers glass-silicone laminates (Type GS). Military procurement requirements include:
- Qualification testing per specification before a supplier may ship mil-spec certified stock
- Lot-level testing with results documented on the Material Test Report (MTR)
- Certificate of Conformance (CoC) issued with each shipment
- Traceability to the laminating run
Drawings calling out MIL-I-24768/17 must be sourced from a DLA-qualified supplier. Confirm QPL (Qualified Products List) status with your supplier before ordering on long-lead programs.
ASTM D709
ASTM D709 covers standard practices for machining, sample preparation, and conditioning of laminated thermosetting materials. It is referenced within both NEMA LI-1 and MIL-I-24768 for test specimen preparation and is useful when specifying acceptance criteria for machined parts made from G7.
Sheet Specifications
Standard Thicknesses
NEMA LI-1 standard thickness increments for G7 sheet:
| Nominal Thickness | Tolerance (±) |
|---|---|
| 0.031 in. | 0.005 in. |
| 0.062 in. | 0.006 in. |
| 0.093 in. | 0.008 in. |
| 0.125 in. | 0.010 in. |
| 0.187 in. | 0.015 in. |
| 0.250 in. | 0.020 in. |
| 0.375 in. | 0.025 in. |
| 0.500 in. | 0.030 in. |
| 0.750 in. | 0.040 in. |
| 1.000 in. | 0.050 in. |
| 1.500 in. | 0.060 in. |
| 2.000 in. | 0.070 in. |
| 3.000 in. | 0.090 in. |
| 4.000 in. | 0.100 in. |
The ±10% rule is a general guide; actual tolerance values at each thickness are enumerated above per NEMA LI-1. Note that tighter thickness tolerances are achievable by post-machining (precision grinding or surface milling) at additional cost and lead time.
Panel Sizes
Standard laminator panel sizes for G7 sheet:
| Width (in.) | Length (in.) | Notes |
|---|---|---|
| 24 | 36 | Common thin-gauge panel |
| 36 | 48 | Standard stocking size |
| 48 | 96 | Full-size panel, thicker gauges |
Non-standard panel sizes (e.g., 24×48, 48×72) are available from select laminators. Very thick slabs (>4 in.) are custom items requiring direct inquiry with the laminator.
Surface Condition
G7 sheet is supplied with one of the following surface conditions:
- Sanded both sides (SBS): Most common for machined-part programs; removes surface resin gloss and provides uniform thickness.
- Unsanded (as-laminated): Slightly higher gloss; used when the laminate surface is not a functional seating surface and where machining stock removal is planned.
Rod Specifications
G7 rod is manufactured by compression molding or by turning from thick sheet. Property values in the rod cross-section may differ slightly from sheet due to the different fiber orientation during fabrication.
Standard Diameters and Lengths
| Nominal Diameter (in.) | Tolerance | Standard Lengths |
|---|---|---|
| 0.250 | +0.015/−0.000 | 4 ft |
| 0.375 | +0.015/−0.000 | 4 ft |
| 0.500 | +0.020/−0.000 | 4 ft, 8 ft |
| 0.750 | +0.025/−0.000 | 4 ft, 8 ft |
| 1.000 | +0.030/−0.000 | 4 ft, 8 ft |
| 1.500 | +0.040/−0.000 | 4 ft |
| 2.000 | +0.050/−0.000 | 4 ft |
| 3.000 | +0.060/−0.000 | 4 ft |
| 4.000 | +0.080/−0.000 | 2 ft |
| 6.000 | +0.100/−0.000 | 2 ft |
Rod diameters above 4 in. are specialty items. Precision-turned rod to closer tolerances (±0.005 in. or better) is available as a machined-part program.
Tube Specifications
G7 tubes (also called cylinders or bobbins) are wound or machined to close tolerance. Standard tube programs:
| ID (in.) | Wall Thickness (in.) | OD (in.) | Length |
|---|---|---|---|
| 0.500 | 0.062 | 0.624 | 12–24 in. |
| 0.750 | 0.062 | 0.874 | 12–24 in. |
| 1.000 | 0.125 | 1.250 | 12–24 in. |
| 2.000 | 0.187 | 2.374 | 12–24 in. |
| 3.000 | 0.250 | 3.500 | 12 in. |
| 4.000 | 0.312 | 4.624 | 12 in. |
Custom ID/OD combinations and lengths are available on program. Wall thickness below 0.062 in. is not recommended for G7 tube due to lamination integrity concerns at thin walls.
Procurement Specification Notes
Commercial Purchase Orders
For commercial NEMA G7 stock, a purchase order should specify:
- Grade: NEMA G7
- Form: Sheet, Rod, or Tube
- Dimensions (thickness/diameter, width, length — or specify standard panel)
- Quantity
- Surface condition (sheet: sanded or unsanded)
- Any supplementary requirements (lot testing, CoC)
Military Purchase Orders
For MIL-I-24768/17 procurement, the purchase order must additionally call out:
- MIL-I-24768/17, Type GS
- Certificate of Conformance per item
- Material Test Report per lot
- DLA/QPL qualified source requirement (if applicable to your program)
- Country of origin (Buy American Act applicability for federal programs)
MIL-I-24768/17 certified G7 stock commands a price premium over commercial NEMA G7 — typically 20–50% depending on lot size — due to the testing and documentation burden. Budget accordingly when writing BOMs for defense programs.
Lead Times
| Item | Typical Lead Time |
|---|---|
| Standard NEMA G7 sheet, stock thicknesses | 1–3 weeks from distributor |
| Standard NEMA G7 rod, stock diameters | 2–4 weeks |
| MIL-I-24768/17 sheet, stock thicknesses | 4–8 weeks |
| MIL-I-24768/17, non-standard thickness | 8–12 weeks |
| Custom tube programs | 6–10 weeks |
| Very thick slabs (>3 in.) | 10–16 weeks |
Lead times are subject to laminator capacity and resin availability. Silicone resins for G7 have a more limited supply base than epoxy resins used in G10 and FR4, so supply disruptions affect G7 more acutely. For long-lead defense programs, safety stock is advisable.
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