G10 threaded rod solves a specific engineering problem that metal fasteners create inside electrical equipment—conductive paths where insulation is required. Switchgear busbar supports, transformer core clamping assemblies, and high-voltage terminal boards all use G10 or FR4 threaded rod to provide mechanical fastening without introducing a ground fault risk or partial discharge site. This guide covers the complete size range from M6 to M20, the tensile and dielectric properties that determine when G10 or FR4 is the correct material choice, how to calculate load capacity for your application, and the ordering specifications that ensure the rods arriving on your receiving dock match the datasheet values you designed around.
What Is G10 Threaded Rod and Where Is It Used in Electrical Equipment?
G10 threaded rod is a continuous fiberglass-reinforced epoxy composite manufactured by pultruding E-glass fibers through an epoxy resin bath and curing the material into a solid cylindrical profile, which is then threaded using standard metric or imperial thread-cutting dies. The pultrusion process aligns the glass fibers parallel to the rod axis, giving G10 rod a tensile strength of 300-400 MPa in the longitudinal direction—comparable to mild steel at one-quarter the weight. The epoxy matrix provides electrical insulation with dielectric strength of 12-16 kV/mm perpendicular to the rod axis and a comparative tracking index exceeding 500V, placing it in the highest PLC category for resistance to surface tracking under contaminated conditions.
Three applications dominate G10 threaded rod demand in the electrical equipment industry. Transformer manufacturers use G10 rods for core clamping bolts where the rod passes through the laminated core and must withstand both the continuous clamping force and the 10-15× rated current short-circuit forces without shearing. Switchgear OEMs specify G10 threaded rod for busbar support assemblies where the rod must carry the weight of copper busbars under continuous current heating to 80-100°C while maintaining sufficient creepage distance between phases. Motor and generator manufacturers use G10 rods for through-bolts in stator core stacking, where the rod’s thermal expansion coefficient of approximately 8-10 × 10⁻⁶/°C—close to that of copper—minimizes differential thermal expansion stress between the clamping bolt and the copper windings it supports. Understanding G10 material equivalents helps procurement teams identify alternative rod materials that meet the same NEMA and IEC specifications when G10 rod is unavailable from a preferred supplier.
What Sizes Are Available? M6, M8, M10, M12, M16, M20 Specifications
G10 threaded rod is manufactured in standard metric thread sizes from M6 to M20 with thread pitches conforming to ISO 724 coarse thread standards. The M6 × 1.0 mm rod—the smallest commonly produced size—has a nominal outer diameter of 6.0 mm and a core diameter of approximately 4.9 mm at the thread root, providing a tensile stress area of 20.1 mm². This size appears most frequently in low-voltage terminal board assemblies and instrument transformer bushings where clamping forces are moderate and the primary requirement is electrical isolation rather than high mechanical load capacity. The customer inquiry from Ho Xin Ru requesting “G10 threaded rod M6 × 1mm, length 1.2m Q2 pc” represents the typical small-quantity prototyping order that precedes production-volume procurement.
M16 and M20 rods serve the heavy structural applications. M20 × 2.5 mm rod has a nominal diameter of 20.0 mm, a stress area of 245 mm², and a tensile breaking load of approximately 73-98 kN (7.4-10.0 tons) depending on the glass content and resin formulation of the specific manufacturer. These larger diameters are used in power transformer core clamping where the clamping assembly must withstand short-circuit forces measured in tons, and in large switchgear busbar supports where the rod may span 500-1,000 mm between support points while carrying distributed copper busbar weight. The same customer inquiry that included M6 rods also specified “M16 × 2mm, length 1.2m Q4 pc” and “M20 × 2.5mm, length 1.2m Q4 pc”—a request pattern that suggests the buyer was prototyping multiple clamping configurations simultaneously across different equipment frame sizes.
| Size | Thread Pitch | Stress Area | Tensile Break | Typical Length | Typical Application |
|---|---|---|---|---|---|
| M6 | 1.0 mm | 20.1 mm² | 6.0 – 8.0 kN | 0.5 – 1.5 m | Terminal boards, instrument transformers |
| M8 | 1.25 mm | 36.6 mm² | 11 – 15 kN | 0.5 – 2.0 m | Small busbar supports, motor through-bolts |
| M10 | 1.5 mm | 58.0 mm² | 17 – 23 kN | 0.5 – 2.0 m | Distribution transformer clamping |
| M12 | 1.75 mm | 84.3 mm² | 25 – 34 kN | 0.5 – 2.0 m | Medium switchgear busbar assemblies |
| M16 | 2.0 mm | 157 mm² | 47 – 63 kN | 0.5 – 2.0 m | Power transformer core clamping |
| M20 | 2.5 mm | 245 mm² | 73 – 98 kN | 0.5 – 2.0 m | Large power transformer, heavy switchgear |
How Much Load Can a G10 Threaded Rod Support?
Tensile load capacity of G10 threaded rod depends on the stress area at the thread root, not the nominal diameter, because the threaded section creates a reduced cross-section where fracture initiates. For a standard M12 × 1.75 mm G10 rod with a stress area of 84.3 mm² and a manufacturer-rated ultimate tensile strength of 350 MPa, the calculated breaking load is 84.3 × 350 = 29.5 kN (approximately 3,010 kg-force). Engineering practice applies a safety factor of 3-5 for static clamping applications and 8-10 for dynamic or short-circuit loading, yielding a recommended working load of 6-10 kN for static use and 3-4 kN for dynamic applications. These working loads assume a clean, undamaged thread surface—thread damage from improper die cutting or handling can reduce the effective load capacity by 20-40% because the stress concentration at a damaged thread root initiates premature fracture well below the calculated breaking load.
The threaded rod supplier should provide batch-specific tensile test data, not a generic datasheet value. Tensile strength varies between manufacturers because the glass-to-resin ratio in the pultrusion process directly affects both strength and machinability. G10 rods with glass content above 70% by weight achieve the highest tensile values (380-420 MPa) but are more difficult to thread cleanly because the glass-rich surface tends to chip at the thread crest during die cutting. Rods with glass content of 60-65% thread more cleanly at tensile values of 300-350 MPa and represent the best balance of strength and thread quality for most electrical equipment applications. Our G10, FR4, G11, and FR5 threaded rods are manufactured with optimized glass content for consistent thread quality while meeting or exceeding the tensile strength values in the table above. Contact jessie.feng@sidanm.com for batch-specific tensile test certificates.
Compressive load capacity—relevant when the rod is used as a spacer or standoff between two clamped surfaces—is approximately 1.5-2× the tensile capacity because the continuous glass fibers resist buckling effectively at the typical length-to-diameter ratios used in electrical equipment (L/D below 20:1). At higher L/D ratios above 50:1, G10 rods become susceptible to Euler buckling, and the compressive capacity should be calculated using the Euler critical load formula with an elastic modulus of 20-25 GPa for the composite material. For the 3240 epoxy glass threaded rod option—the Chinese GB-grade equivalent—the tensile and compressive properties are comparable to G10 though the buyer should verify batch consistency through incoming inspection as quality control standards differ between manufacturers producing to GB/T versus NEMA specifications.
What Is the Difference Between G10 and FR4 Threaded Rod?
The primary distinction between G10 and FR4 threaded rod is flame retardancy—not mechanical properties. FR4 rod contains brominated flame retardant additives in the epoxy resin formulation, achieving a UL 94 V-0 flammability rating. G10 rod uses non-flame-retardant epoxy, typically achieving only UL 94 HB classification. The glass fiber reinforcement, fiber orientation, and pultrusion process are identical between the two grades, so tensile strength, flexural modulus, and dielectric properties differ by less than 5% between G10 and FR4 of the same manufacturer and glass content. The flame retardant additives in FR4 slightly increase the dissipation factor at elevated frequencies—approximately 0.018-0.022 at 1 MHz for FR4 versus 0.015-0.018 for G10—a negligible difference for 50/60 Hz power applications but potentially significant for radio-frequency equipment where the rod functions as an insulating standoff in antenna or transmitter assemblies.
The procurement decision between G10 and FR4 rod should be driven by the end-product certification requirements, not by a general preference for flame-retardant materials. Equipment destined for North American markets where UL listing requires V-0 rated insulation materials throughout the assembly must use FR4 threaded rod. Equipment for IEC markets where internal components are accepted under IEC 60695-11-10 with HB classification can use the lower-cost G10 rod while achieving identical mechanical and electrical performance. Using FR4 where G10 is acceptable adds approximately 10-15% to the rod material cost without a corresponding performance benefit. The same logic applies when comparing FRP threaded rod alternatives—polyester-glass rods provide a further cost reduction below G10 pricing but with lower thermal capability (Class B, 130°C versus Class F, 155°C for G10/FR4) and higher moisture absorption that limits their use to dry, indoor applications.
Threaded rod material selection becomes an exercise in matching the rod’s properties to the specific environmental and electrical stresses of the application. G10 or FR4 rods perform identically in clean, dry, indoor electrical equipment—the choice reduces to certification requirements. For outdoor equipment exposed to UV radiation or condensation, both G10 and FR4 require additional surface protection because epoxy resins degrade under prolonged UV exposure, causing surface chalking and reduced tracking resistance over 5-10 years of outdoor service. For applications requiring continuous operation above 155°C, G11 rod (180°C thermal class) or silicone-bonded glass rod should replace G10/FR4 entirely.
How to Order Custom Threaded Rod Sizes and Lengths
Custom threaded rod orders require four specifications that standard stock rod purchases do not: thread length, unthreaded shank length, chamfer requirement, and thread fit class. Standard G10 rod stock typically ships with full-length threading, but many electrical equipment designs require a partially threaded rod—threaded at both ends for nut engagement with an unthreaded center section that passes through the insulated component. The thread length on each end must be specified as the distance from the rod end plus the thread run-out zone of approximately 1-2 thread pitches where the thread depth transitions from full to zero. Insufficient specified thread length results in nuts that bottom out on the thread run-out rather than seating against the intended clamping surface.
Thread fit class determines the clearance between the external rod thread and the internal nut thread, affecting both assembly ease and vibration resistance. Standard metric thread fit 6g/6H provides adequate clearance for hand assembly while maintaining thread engagement of approximately 75%—sufficient for static clamping applications. For applications subject to vibration—generator through-bolts, traction motor clamping, marine electrical equipment—specifying a tighter fit class 4g/4H or requesting a prevailing-torque locking feature such as a nylon insert lock nut or thread-locking compound on the rod threads prevents the gradual loosening that vibration-induced precession causes in standard-fit threaded assemblies. Our nylon threaded rod option provides an alternative where the application requires a fully non-metallic threaded fastener with inherent vibration resistance from the nylon material’s damping properties, albeit at significantly lower tensile strength (50-80 MPa) than G10/FR4.
The sample-test-buy sequence that SIDA recommends for first-time G10 rod purchasers follows the pattern demonstrated by the Alexandre ROGER case: request 2-3 sample rods in the required diameter and thread specification, perform fit-check with the intended nuts and assembly tooling, verify tensile break load on a sample rod from each production batch, and then place a production order once the samples confirm dimensional and mechanical compliance. This sequence typically requires 2-3 weeks from sample request to production order and prevents the costly scenario of receiving production-quantity rods that thread differently from what the design team assumed based on a generic datasheet. Contact jessie.feng@sidanm.com or call +86-15958243831 to request G10/FR4 threaded rod samples with dimensional inspection reports and tensile test data from the production batch.
Frequently Asked Questions About G10/FR4 Threaded Rod
Can G10 threaded rod be cut to length after threading?
Yes, but with two critical precautions. Cutting a fully threaded G10 rod mid-length with a hacksaw or abrasive cutoff wheel produces a burred thread end that will cross-thread when attempting to engage a nut, unless the cut end is re-chamfered using a file or grinding wheel to restore the thread lead-in angle of approximately 15-20 degrees. The heat generated during abrasive cutting can degrade the epoxy resin at the cut surface to a depth of 0.5-1.0 mm, reducing the thread strength in that localized zone. Flood-cooling the cut with water or using a diamond-grit blade at low feed rate minimizes this thermal damage. For production applications requiring consistent cut-to-length rods, the supplier should provide rods cut and re-chamfered during manufacturing rather than relying on jobsite cutting.
Do G10 threaded rods require special nuts or washers?
Standard metric hex nuts and flat washers in steel, brass, or stainless steel are compatible with G10 threaded rod for the majority of electrical equipment applications. The mating nut material should be selected based on the operating environment rather than compatibility concerns with the rod itself. Galvanized steel nuts are adequate for indoor, dry applications. Stainless steel (304 or 316 grade) nuts should be used in outdoor or high-humidity environments to prevent nut corrosion that could seize the threaded joint. Nylon or G10 nuts provide a fully non-metallic fastening system where even the nut must be electrically insulating—for example, in high-voltage busbar supports where a metal nut could create a local field concentration that reduces the creepage distance between phases below the design minimum.
What is the typical lead time for custom G10 threaded rod orders?
Standard stock sizes—M6, M8, M10, M12 in 1-meter lengths with full-length threading—typically ship within 2-5 business days from inventory. Custom diameters (M14, M18, or imperial sizes), custom lengths, or partial-length threading add 7-14 business days for production setup and threading. Production quantities exceeding 500 pieces may require 14-21 business days depending on the pultrusion production schedule. Expedited service with 5-7 business day turnaround is available for custom orders with an urgency surcharge of 15-25% of the order value. Buyers with recurring annual requirements should consider a blanket purchase order with scheduled releases to lock in both pricing and production capacity.
How should G10 threaded rods be stored to prevent damage?
Store G10 threaded rods horizontally on padded racks that support the rod at multiple points along its length—never leaned against a wall or rack where the rod’s own weight creates a bending moment that can induce micro-cracks in the epoxy matrix. Threads should be protected with plastic thread caps or the rods should be individually wrapped in VCI (volatile corrosion inhibitor) paper for rods with partial-length threading where the unthreaded section is the primary structural element. Avoid stacking heavy items on top of stored rods—the compressive creep of the epoxy matrix under sustained point loading can create permanent thread deformation that prevents nut engagement. Storage temperature should remain below 50°C to prevent accelerated thermal aging of the epoxy resin, though G10 rods tolerate intermittent exposure up to 130°C without permanent degradation of mechanical properties.
Summary: Specifying G10/FR4 Threaded Rod for Reliable Electrical Equipment
G10 threaded rod combines the tensile strength of mild steel with the electrical insulation of epoxy-glass laminate, solving the fundamental problem of mechanical fastening inside energized electrical equipment. Standard metric sizes from M6 to M20 with coarse ISO threads cover the full range from instrument transformer terminal boards (M6) to power transformer core clamping assemblies (M20). The choice between G10 and FR4 reduces to flame retardancy certification requirements—not mechanical performance differences. Batch-specific tensile test data from the rod manufacturer matters more than the grade designation because glass-to-resin ratio and pultrusion process control determine the actual strength of the rods on your receiving dock. The sample-test-buy qualification sequence prevents the production disruptions caused by receiving rods that thread differently or break differently than expected.
SIDA supplies G10, FR4, G11, and FR5 threaded rods in diameters from M6 to M20 with full or partial-length threading, chamfered ends, and batch-specific tensile test certification. Our threaded rod products integrate with a complete non-metallic fastener portfolio including nylon and FRP options for applications where the material requirements differ from epoxy-glass composites. Request threaded rod samples with dimensional inspection and tensile test reports from jessie.feng@sidanm.com or call +86-15958243831. Product datasheets and our complete threaded rod catalog are available at sidanm.com.
