What Is an FRP Nut?
An FRP nut (Fiber Reinforced Plastic nut) is a non-metallic structural fastener manufactured from fiberglass rovings embedded within a thermoset resin matrix — typically polyester, vinyl ester, or epoxy. The composite construction delivers high corrosion resistance, full electrical insulation, and a significant weight reduction compared to steel or stainless steel equivalents, without compromising the mechanical load performance required in engineered assemblies.
FRP nuts are specified where metal fasteners are technically unsuitable: aggressive chemical media, saltwater immersion, high-voltage electrical environments, and weight-critical composite structures.
Our FRP nuts is manufactured by pultrusion for consistent quality. Related FRP solutions: pultruded FRP profiles, FRP rebar, pultrusion machines, and pultrusion dies.
Types of FRP Nuts
FRP Hex Nut
Standard hexagonal profile, dimensionally compatible with conventional spanner and torque wrench tooling. Manufactured in metric thread sizes M6–M24 and imperial equivalents. Used with matching FRP bolts or stainless steel threaded rod in structural framing, GRP grating, and chemical plant pipework supports.
FRP Square Nut
Broader bearing surface than the hex profile; provides high resistance to pull-through and rotation in panel and framing systems. Available M8–M24. Commonly specified in GRP walkway and modular structural systems.
FRP Binding Nut (Panel / Trailer Type)
A flanged nut with a 6-lobe (Torx-compatible) drive, engineered for high-speed power tool assembly of FRP wall and floor panels to steel or aluminium trailer chassis rails. The integral flange distributes clamping load across the panel face, reducing stress concentration and the risk of composite delamination at the fastener hole.
Pultruded FRP Nut
Produced via continuous pultrusion for tight dimensional tolerances and controlled fibre-to-resin ratio. Available in custom thread sizes and non-standard profiles. Preferred in precision electrical switchgear and thermal insulation assemblies.
Technical Properties & Material Data
| Property | Value |
|---|---|
| Base Material | E-glass fibre / thermoset resin composite |
| Resin System Options | Polyester · Vinyl ester · Epoxy |
| Fibre Content (by weight) | 40–70% depending on grade |
| Tensile Strength | 80–200 MPa |
| Flexural Strength | 150–300 MPa |
| Compressive Strength | 100–250 MPa |
| Shear Strength | 30–60 MPa |
| Density | 1.6–2.0 g/cm³ (vs. 7.85 g/cm³ for carbon steel) |
| Hardness | Barcol 40–60 |
| Operating Temperature | –30°C to +140°C (standard) · up to +180°C (high-temp resin) |
| Thermal Conductivity | 0.3–0.5 W/m·K |
| Coefficient of Thermal Expansion | 14–20 × 10⁻⁶/°C |
| Dielectric Strength | 10–25 kV/mm |
| Volume Resistivity | >10¹² Ω·cm |
| Water Absorption (24h) | <0.3% |
| Flame Rating | UL94 HB / V-0 (halogen-free grade) |
| UV Resistance | Stabilised resin options available |
| RoHS Compliance | Yes |
Dimensional Specifications
Standard Metric Hex Nut — FRP
| Thread Size | Width Across Flats (mm) | Nut Height (mm) | Pitch (mm) |
|---|---|---|---|
| M6 | 10 | 5.0 | 1.0 |
| M8 | 13 | 6.5 | 1.25 |
| M10 | 17 | 8.0 | 1.5 |
| M12 | 19 | 10.0 | 1.75 |
| M16 | 24 | 13.0 | 2.0 |
| M20 | 30 | 16.0 | 2.5 |
| M24 | 36 | 19.0 | 3.0 |
Binding Nut (Panel / Trailer Type) — Imperial
| Parameter | Value |
|---|---|
| Thread Size | 5/16″-18 UNC |
| Nut Length | 3/8″ – 5/8″ |
| Flange OD | 1 in. |
| Drive | 6-lobe (Torx-compatible) |
| Grade | 5.1 (cold formed & heat treated) |
| Recommended Torque | 8–12 N·m (verify per panel substrate) |
| Packing | 10 / 25 / 50 / 100 pc bulk |
Chemical Resistance Reference
| Medium | Resistance |
|---|---|
| Sulfuric acid (H₂SO₄) ≤50% | Excellent |
| Hydrochloric acid (HCl) ≤35% | Excellent |
| Sodium hydroxide (NaOH) ≤40% | Good |
| Seawater / brine | Excellent |
| Diesel / mineral oils | Excellent |
| Acetone / ketones | Limited — verify with supplier |
| Concentrated oxidising acids | Not recommended |
Resin system selection significantly affects chemical resistance. Vinyl ester and epoxy systems generally outperform standard polyester in aggressive media. Always confirm compatibility for continuous immersion service.
Application Engineering Notes
Chemical & Water Treatment Plants
Vinyl ester or epoxy FRP nuts are the standard specification for pipework, tank supports, and filter press assemblies handling acids, chlorine dosing systems, and caustic soda. Reduces corrosion-driven maintenance cycles and avoids metal ion contamination of process streams.
Truck Body & Trailer Manufacturing
The FRP binding nut is the production-line standard fastener for FRP composite wall and floor panel attachment to steel or aluminium rails. The 6-lobe drive maintains drive engagement under high-torque pneumatic installation. Flange geometry prevents countersink pull-through in thin-skin panel assemblies.
Electrical Infrastructure
Specified in transformer mounting frames, busbar support structures, cable tray systems, and HV switchgear panels. Dielectric strength of 10–25 kV/mm provides the electrical isolation margin required by IEC and NEMA standards. Eliminates the conductivity risk inherent in stainless steel fasteners in live panel environments.
Marine & Offshore
Galvanically compatible — no bi-metallic corrosion risk when used with aluminium or composite structures. Suitable for continuous saltwater immersion with appropriate resin system. Widely used in GRP vessel construction, jetty hardware, and offshore platform walkways.
Food & Pharmaceutical Processing
No rust, no metal ion migration. Compatible with steam clean-down and CIP wash cycles. Suitable for hygiene-focused ancillary structures when specified appropriately.
FRP Nut vs. Alternative Materials
| Property | FRP | 316 Stainless Steel | Carbon Steel (HDG) | PEEK |
|---|---|---|---|---|
| Corrosion resistance | Excellent | Good (pitting risk in Cl⁻) | Moderate | Excellent |
| Electrical insulation | Yes | No | No | Yes |
| Weight (relative) | Low | High | High | Low |
| Temp. range | –30 to +140°C | –200 to +870°C | –40 to +400°C | –60 to +250°C |
| Cost (relative) | Low–Medium | Medium–High | Low | Very High |
| Galvanic neutrality | Fully inert | Active (risk) | Active (risk) | Fully inert |
| Magnetic | No | No (austenitic) | Yes | No |
Frequently Asked Questions
Q: What is the torque rating for FRP nuts?
A: Torque capacity depends on thread size, resin system, and fibre content. As a reference, a standard M12 FRP hex nut in vinyl ester resin carries a maximum recommended torque of approximately 18–22 N·m. For binding nuts (5/16″-18 UNC), the recommended installation torque is typically 8–12 N·m. Over-torquing will cause fibre delamination at the thread root — always use a calibrated torque wrench for critical joints.
Q: Can FRP nuts be used in continuous immersion service?
A: Yes, provided the correct resin system is selected. Vinyl ester and epoxy-based FRP nuts are rated for continuous immersion in most dilute acid, alkali, and saline environments. Standard polyester systems are acceptable for splash and intermittent exposure. Water absorption over 24 hours is typically below 0.3%, ensuring minimal dimensional change in service.
Q: Are FRP nuts suitable for structural load-bearing connections?
A: FRP nuts are designed for the load requirements of composite and FRP structural systems, not as direct substitutes for high-grade structural steel bolting (Grade 8.8 / 10.9). Tensile strength ranges from 80–200 MPa depending on grade. Always specify to your structural engineer for safety-critical connections.
Q: What is the maximum service temperature?
A: Standard FRP nuts operate continuously from –30°C to +140°C. High-temperature resin systems (typically epoxy-based) extend the upper limit to +180°C. For applications exceeding this range, PEEK or ceramic fasteners should be considered.
Q: Can FRP nuts be used with metal bolts?
A: Yes. FRP nuts are compatible with stainless steel, carbon steel, and FRP bolts. For fully non-conductive assemblies — such as HV electrical panels — matched FRP bolt and nut sets are required to eliminate all metallic contact paths.
Q: Do FRP nuts require anti-seize compounds?
A: Anti-seize is not required as FRP does not corrode or gall. However, a small amount of non-conductive thread lubricant can be used in controlled-torque assemblies to improve installation consistency and reduce friction scatter in torque readings.
Q: How do I identify the correct resin system for my application?
A: Review the chemical resistance table above as a first reference. For continuous immersion in HCl, H₂SO₄, or oxidising environments, specify vinyl ester or epoxy resin. For standard corrosion protection in atmospheric or saline exposure, polyester resin is cost-effective and adequate. Always confirm with your supplier for critical service conditions.
Q: Are FRP nuts UV-stable for outdoor installation?
A: Standard FRP nuts have acceptable outdoor durability. For prolonged direct UV exposure, specify UV-stabilised resin grades — particularly for white or light-coloured nuts where surface chalking and micro-cracking are more visible over time.
Pair these nuts with our FRP bolts for a fully non-metallic, corrosion-proof fastening set.
Request a Quote for FRP Nuts
Need FRP nuts for your project? Contact us for a quote and we will confirm specifications, lead time, and pricing.
