Quick Answer
G10 and FR4 washers are CNC-machined from epoxy fiberglass laminate sheets. They provide electrical isolation and galvanic corrosion protection between bolts and mating surfaces in electrical panels, busbars, switchgear, and assemblies with dissimilar metals. Standard or custom ID × OD × thickness washers and spacers can be produced from drawings, with typical continuous-use temperatures around 130 °C (266 °F) for standard NEMA grades; high-performance or thicker grades may differ.
Looking for the full custom washer range, including G11/FR5 high-temperature grades and shoulder washers? Visit the custom insulating washers hub.
Overview
Washers made from G10 and FR4 are cut or CNC-machined from NEMA-grade epoxy fiberglass laminates rather than molded or pultruded. This gives them consistent thickness, high dimensional stability, and good electrical insulating properties. They are widely used where metal washers would create a short circuit, galvanic cell, or corrosion path.
Common applications include transformer and motor terminal insulation, busbar isolation, switchgear and panel board mounting, battery rack connections, and assemblies where aluminum frames meet stainless-steel or galvanized hardware. In these cases the washer acts as a thin, load-spreading insulator that also prevents metal-to-metal contact.
G10 and FR4 are similar materials. Both are based on woven glass fabric bonded with epoxy resin. FR4 includes a flame-retardant additive that meets the requirements of the NEMA FR4 grade, while G10 is the general-purpose grade. For many washer and spacer applications the mechanical and electrical properties are comparable, but FR4 is preferred when flame retardancy is specified.
Material Grades and Standards
NEMA (National Electrical Manufacturers Association) defines the grades most commonly used for epoxy fiberglass laminates in North America. G10 is specified under NEMA LI 1, while FR4 belongs to the same laminate family with added flame-retardant requirements. These standards set minimum mechanical, electrical, and thermal performance expectations, but they do not guarantee identical values across all thicknesses or suppliers.
When placing an order, the drawing or purchase order should state the required grade, sheet thickness, and any flame or electrical requirements. If the assembly must satisfy a local electrical or fire safety code, the end customer should confirm that the supplier documentation supports that code.
FR4 vs G10 for Washers
| Property | G10 | FR4 |
|---|---|---|
| Base material | Epoxy fiberglass laminate (NEMA G10) | Epoxy fiberglass laminate (NEMA FR4) |
| Flame retardancy | Not rated flame-retardant | Flame-retardant grade |
| Typical continuous-use temperature | NEMA Class B, typically ~130 °C (266 °F); confirm with datasheet | NEMA Class B, typically ~130 °C (266 °F); confirm with datasheet |
| Mechanical strength | High compressive and flexural strength | High compressive and flexural strength |
| Electrical insulation | Good electrical isolation in dry conditions | Good electrical isolation in dry conditions |
| Common names | G10, Garolite G10 | FR4 |
| Typical use case | General electrical isolation, spacers, custom gaskets | Applications requiring flame-retardant material |
Specific values for dielectric strength, glass transition temperature, and flame rating vary by manufacturer and laminate batch. Request a material datasheet for applications governed by standards or safety codes.
Specifications and Available Sizes
G10 and FR4 washers are produced to drawing rather than selected from a fixed catalog. CNC machining allows small to medium batches with tight tolerances. Common dimensions include:
- Inner diameter (ID): from approximately 4 mm (5/32 in) to over 50 mm (2 in), matching standard bolt sizes.
- Outer diameter (OD): typically 1.5 to 3 times the bolt diameter, or per drawing.
- Thickness (T): commonly 0.5 mm to 6 mm (0.020 in to 0.25 in); thicker spacers and sleeves are also available.
- Tolerances: ±0.1 mm to ±0.3 mm depending on diameter and thickness; tighter tolerances quoted on request.
- Finish: natural green/yellow-brown laminate color; edges are clean-cut and free of delamination.
Because laminate sheets are purchased in standard thicknesses, custom washers are normally sourced from the closest available sheet thickness and finished to final dimensions. Provide a drawing or sample for exact matching.
Machining and Tolerances
The abrasive glass content in G10 and FR4 means that carbide or diamond tooling is normally used for machining. High-speed steel tools wear quickly and can leave frayed edges or poor dimensional control.
- CNC routing and milling: Best for flat washers, profiled spacers, and complex shapes. Multi-pass cutting and proper chip evacuation reduce edge delamination.
- Punching: Economical for large quantities of simple round washers in thinner sheets. Tool clearance must match sheet thickness to avoid cracking.
- Drilling and reaming: Used for precise holes. Backup plates and controlled feed rates help prevent breakout on the exit face.
- Deburring: Edges are lightly deburred after machining to remove glass fibers and resin burrs that could affect assembly fit.
IncomePultrusion machines G10 and FR4 washers, spacers, sleeves, and standoffs from customer drawings. Provide the grade, thickness, dimensions, quantity, and tolerance requirements when requesting a quote.
Applications
- Electrical panels and switchgear. Insulating washers prevent grounding paths and reduce the risk of short circuits between live components and frames.
- Busbar and battery connections. Non-conductive washers isolate copper or aluminum busbars from steel hardware.
- Motor and transformer terminals. Thin washers maintain creepage and clearance distances in compact assemblies.
- Dissimilar-metal assemblies. G10/FR4 washers block galvanic corrosion between aluminum, stainless steel, or galvanized parts.
- Custom spacers and standoffs. CNC machining can produce not only flat washers but also tubular spacers and sleeved bushings from the same laminate.
How G10/FR4 Washers Differ from Pultruded FRP Washers
IncomePultrusion supplies both laminate G10/FR4 washers and pultruded FRP washers, but the two product families serve different needs.
- G10/FR4 washers are machined from epoxy fiberglass laminate sheets. They are most often specified for electrical isolation and controlled thickness in static assemblies.
- Pultruded FRP washers are made from continuous glass-fiber profiles and are used in corrosive environments such as chemical plants, water treatment facilities, and offshore structures where the washer must resist salt, acids, and alkalis. See the FRP washers guide and the FRP washer product page for details.
If the application requires both electrical isolation and long-term chemical resistance, share the operating conditions so the appropriate material and grade can be recommended.
Quality and Inspection
Before packing, each batch of G10 and FR4 washers is checked for dimensional accuracy, edge condition, and visual defects. Typical inspections include ID, OD, thickness, surface finish, and freedom from cracks, voids, or delamination.
Mechanical and electrical properties are verified against supplier datasheets and internal benchmarks. When a project requires batch test reports, material traceability, or custom inspection plans, these are agreed at the quotation stage and documented with the shipment.
Custom CNC and How to Request a Quote
To quote G10 or FR4 washers, the following information is needed:
- Material grade: G10 or FR4
- Inner diameter, outer diameter, and thickness, or a dimensional drawing
- Quantity per batch and annual volume
- Tolerance requirements
- Operating temperature and any flame-retardant or electrical specifications
- Whether washers, spacers, sleeves, or a mixed kit are required
Submit these details through the quote request page. IncomePultrusion can machine prototypes for validation before moving to production quantities.
Frequently Asked Questions
What is the difference between FR4 and G10 washers?
Both are epoxy fiberglass laminates. FR4 includes a flame-retardant additive and meets the NEMA FR4 grade, while G10 is the general-purpose grade. For washer and spacer use the mechanical properties are similar, but FR4 is specified when flame retardancy is required.
Is G10 the same as Garolite?
Garolite is a commercial brand name for glass-reinforced epoxy laminates, including G10. The material properties depend on the specific grade and manufacturer, so a datasheet should be reviewed for critical applications.
Are FR4/G10 washers electrically insulating and non-conductive?
Yes, in dry conditions G10 and FR4 act as electrical insulators and are non-conductive. They are commonly used to isolate bolts from metal frames, busbars, and panels. Surface contamination or moisture can reduce insulating performance, so sealed or clean assemblies are recommended for high-voltage use.
How do FR4/G10 washers differ from pultruded FRP or fiberglass washers?
FR4/G10 washers are machined from flat laminate sheets and are typically chosen for electrical isolation and precise thickness. Pultruded FRP washers are produced from continuous fiber profiles and are selected for corrosion resistance in chemical, marine, and industrial environments. The two materials should not be treated as interchangeable without reviewing the application requirements.
Can you machine custom ID, OD, and thickness?
Yes. G10 and FR4 washers are normally produced by CNC machining or punching from laminate sheet. Custom diameters and thicknesses are quoted from drawings or samples.
What information do you need for a quote?
Provide material grade (G10 or FR4), ID, OD, thickness, quantity, tolerance, operating temperature, and any flame or electrical requirements. A drawing or sample speeds the quotation process.
What temperature range can G10 washers typically handle?
Standard NEMA G10 and FR4 laminates are typically rated for continuous electrical service around 130 °C (266 °F). Actual limits depend on grade, thickness, load, and exposure time. Confirm with the material datasheet for the specific batch.
Do you also supply G10 spacers and sleeves?
Yes. In addition to flat washers, G10 and FR4 can be machined into tubular spacers, sleeved bushings, and custom standoffs. Provide dimensions or a drawing for quotation.
Request a Quote for G10 & FR4 Washers
Submit specifications for custom G10 or FR4 washers, spacers, or sleeves through the quote request page. For projects that also need corrosion-resistant hardware, see the FRP fasteners overview for matching bolts, nuts, and washers.