What Are FRP Screws?
FRP screws are threaded fasteners manufactured from fiber-reinforced polymer composites, typically E-glass or S-glass fibers embedded in a vinyl ester, epoxy, or polyester matrix. They perform the same clamping and joining functions as metal screws but without the corrosion, conductivity, or weight penalties associated with steel, stainless steel, or aluminum.
The manufacturing process starts with pultruded FRP rod stock. Continuous fibers are drawn through a resin bath and formed in heated dies to create a high-fiber-volume profile. The rod is then cut to length and machined—either by CNC threading or precision grinding—to produce machine threads, self-tapping threads, or custom thread forms. This method yields fiber alignment above 60% along the shank and void content below 1%, giving consistent mechanical properties across production lots.
Compared with steel screws, FRP screws are approximately 75% lighter and electrically non-conductive. They do not corrode in saltwater, acids, or alkalis, and they eliminate galvanic coupling when used with aluminum, carbon fiber, or stainless steel components. The trade-off is lower shear strength: designers typically size FRP screws at 50% to 70% of the equivalent steel torque and apply a safety factor of at least 1.5.
FRP screws are part of the broader FRP fasteners family offered by IncomePultrusion. For buyers evaluating a full fastening system, the main hub guide covers bolts, nuts, threaded rods, and washers in detail.
Types of FRP Screws
IncomePultrusion supplies several screw configurations to match different assembly methods and load requirements.
Machine Screws
Machine screws have uniform threads and are used in pre-tapped holes or with FRP nuts. They are available in diameters from M4 to M20 and lengths from 12 mm to 150 mm. These screws are the default choice for electrical enclosures, instrument panels, and light structural joints where precise clamp load is required.
Self-Tapping Screws
Self-tapping FRP screws form their own threads in pre-drilled holes in FRP panels, plastics, or wood. They reduce assembly time because no tapping operation is needed. Common head styles include pan head, countersunk head, and hex washer head. Typical diameters range from M4 to M12.
Hex Head Screws
Hex head screws provide a larger wrenching surface and are preferred for applications requiring higher torque or repeated assembly. They are often used with FRP washers to spread clamp load and prevent surface crushing. Sizes range from M6 to M20.
Custom Thread Forms
For specialized equipment, we manufacture screws with modified thread pitches, left-hand threads, or mixed fiber reinforcement. Custom orders require a minimum quantity and typically add 2 to 4 weeks to the standard lead time.
Key Performance Properties
Mechanical Performance
The mechanical properties of FRP screws depend on fiber grade, resin system, and thread geometry. Typical values for E-glass/vinyl ester machine screws are:
- Tensile strength: 400 MPa to 700 MPa along the fiber axis
- Shear strength: 180 MPa to 280 MPa
- Compression strength: 250 MPa to 350 MPa
- Modulus of elasticity: 25 GPa to 35 GPa
Threads machined across the fiber direction have lower shear capacity than the shank. For this reason, self-tapping screws are recommended for light-duty applications, while machine screws or hex head screws are preferred for structural loads.
Corrosion Resistance
FRP screws do not rust or pit. In ASTM B117 salt-spray testing, vinyl ester formulations regularly exceed 3,000 hours without visible degradation. They also resist dilute acids, alkalis, and chlorinated environments where stainless steel would suffer crevice corrosion.
Electrical Insulation
With a volume resistivity of approximately 10¹⁵ ohm·cm and dielectric strength of 10 kV/mm to 20 kV/mm, FRP screws provide effective electrical isolation. They are non-magnetic and RF transparent, making them suitable for switchgear, transformers, and instrumentation housings.
Weight Comparison
The density of E-glass FRP is approximately 1.9 g/cm³, compared with 7.85 g/cm³ for steel. A box of 1,000 M6 FRP screws weighs roughly 1.2 kg, while the same quantity in steel weighs about 5 kg. The reduction simplifies transport, overhead installation, and manual assembly.
Typical Applications
Chemical Processing Equipment
FRP screws secure flanges, access panels, and instrumentation covers on tanks, scrubbers, and piping systems. In chlorine and acid environments, they avoid the contamination and corrosion products that metal screws introduce into process streams.
Marine and Offshore Platforms
Deck panels, composite grating, and equipment enclosures on offshore platforms are exposed to salt spray and immersion cycles. FRP screws eliminate the seasonal replacement schedules common with plated steel hardware.
Electrical Cabinets and Switchgear
The non-conductive property of FRP screws makes them ideal for busbar covers, terminal blocks, and enclosure assembly. They prevent accidental grounding and reduce arc-flash risks in medium-voltage equipment.
Wastewater Treatment Facilities
Sulfide-rich atmospheres and chemical dosing areas accelerate corrosion of metal fasteners. FRP screws maintain clamp load in pump stations, odor-control units, and filter press assemblies with minimal maintenance.
How to Choose FRP Screws
Selection starts with the application load and environment, then narrows to thread form and resin system.
- Thread type: Use machine screws for tapped metal or FRP holes; use self-tapping screws for through-hole assembly in panels; use hex head screws where higher torque or repeated access is needed.
- Resin system: Vinyl ester offers the best chemical resistance and is the standard for marine and chemical applications. Epoxy provides higher mechanical strength and is preferred for structural loads. Polyester is cost-effective for dry, low-load environments.
- Size range: Common inventory covers M4 to M20. For diameters above M20 or lengths above 150 mm, consider FRP bolts or threaded rods instead.
- Installation torque: Limit tightening torque to 50% to 70% of the equivalent steel value. Use a calibrated torque wrench and padded tooling to avoid thread damage.
Beyond the basic categories, some applications benefit from hybrid reinforcement or specialized surface treatments. Carbon-fiber-reinforced screws offer higher stiffness for instrumentation fixtures, while UV-stabilized surface veils extend outdoor service life. For submerged or splash-zone service, vinyl ester remains the preferred resin because of its low water absorption and resistance to hydrolysis.
Related Resources
- FRP Fasteners Guide — overview of bolts, nuts, screws, rods, and washers
- FRP Threaded Rods — composite anchors and tie rods
- FRP Washers — non-conductive washers for load distribution
- FRP Fastener Product Catalog — browse the full fastener range
- Nylon screws — non-conductive PA66 fasteners for electrical assemblies
For a broader comparison of FRP fastening options, return to the FRP fasteners guide. To check stock sizes and request pricing, browse the FRP fastener product catalog.
Request a quote with your screw specification—diameter, length, thread type, head style, quantity, and resin preference—and we will confirm lead time and test documentation.
