GB/T 802.3 Flange Domed Cap Nut

Core Features
Flanged Base – The flange is integrally formed at the base of the nut, providing a load-bearing surface that distributes clamping force across a wider area compared to standard nut configurations.
Domed Cap Enclosure – The closed cap geometry covers the exposed bolt end, providing a physical barrier against contact with external objects and personnel.
Welding-Type Configuration – The flange geometry includes projection features designed for controlled weld formation when using resistance welding or projection welding processes, enabling permanent attachment to workpiece surfaces.

Product Characteristics
The fastener is produced in accordance with the dimensional and mechanical specifications defined in GB/T 802.3-2009. Thread dimensions and tolerances follow standard metric thread profiles. The flange underside incorporates a contact surface profile designed to maintain consistent clamping force distribution. The domed cap is formed without openings, providing complete coverage of the bolt termination point. Material composition and heat treatment processes are controlled to meet the mechanical property requirements for each specified performance grade.

The projection features on the flange base are dimensioned to support consistent weld formation. The flange geometry includes defined projection height, diameter, and positioning parameters that affect electrode contact area and heat generation during the welding process.

Surface treatment options include zinc plating, nickel plating, chrome plating, and Dacromet coating, each applied according to defined coating thickness and corrosion resistance parameters. Surface treatment selection is determined by the environmental exposure conditions and service life requirements of the application.

Application Scenarios
Industrial Equipment – Used in machinery where exposed bolt ends require mechanical protection and where contaminants such as lubricants, particulates, or process fluids are present. The welding-type configuration provides fixed attachment for components that do not require disassembly.

Automotive Manufacturing – Applied in body-in-white assembly, frame construction, and underbody components where flush-profile fastening reduces protrusion height and where welded attachment provides joint permanence and load distribution.

Public Infrastructure – Installed in handrails, guardrails, access covers, and public seating where fastener protrusion presents contact hazards, and where the domed cap reduces potential injury risk in pedestrian areas.

Agricultural and Construction Equipment – Employed in heavy machinery subject to vibration and cyclic loading, where welded attachment prevents loosening from dynamic forces and the flange provides load distribution, and the cap protects fasteners from dirt and moisture exposure.

Customization Options

Specifications and configurations can be adjusted based on application requirements. Material grades include carbon steel grades for general mechanical applications and stainless steel grades A2 and A4 for corrosion-resistant requirements. Surface treatments are selectable according to environmental exposure conditions, including coatings for salt spray resistance, chemical resistance, or aesthetic requirements. Strength grades can be matched to specific tensile and yield strength criteria defined in the application engineering specifications.

Frequently Asked Questions

Q: What is the difference between GB/T 802.3 and GB/T 802.1?
A: GB/T 802.1 refers to the general specification for cap nuts, covering standard configurations without welding features. GB/T 802.3 specifically covers the welding-type configuration, incorporating projection features on the flange base for weld formation and permanent attachment.

Q: Can these nuts be supplied in non-standard thread sizes?
A: Thread sizes outside the standard M4 to M24 range can be manufactured upon request, subject to tooling availability and minimum order quantity requirements. Custom dimensional specifications are evaluated on a per-order basis.

Q: Are these nuts reusable after welding?
A: The welding-type configuration is intended for permanent installation. Once welded, removal typically requires destructive methods such as grinding or cutting. For applications requiring removal capability, the standard non-welding type cap nut configuration is recommended.

Q: What welding methods are compatible with this product?
A: Resistance welding and projection welding are the commonly used methods for GB/T 802.3 welding-type nuts. The flange geometry includes projection features designed for controlled weld formation when using these processes. Welding parameters should be set based on material grade, thickness, and equipment specifications.

Q: What is the purpose of the domed cap?
A: The domed cap covers the exposed bolt end, providing mechanical protection for the fastener and preventing contact with the bolt end. It also functions as a barrier that reduces the risk of mechanical injury in areas with personnel access.

Q: How do I select the appropriate performance grade for my application?
A: Performance grade selection is determined by the required tensile strength, yield strength, and hardness for the joint design. Grade 6 and 8 apply to carbon steel materials with defined proof load and tensile strength ranges. Grade A2 and A4 designate stainless steel material categories, with A2 for general corrosion-resistant applications and A4 for marine or chemically aggressive environments. The suffix numbers 50 and 70 indicate the tensile strength class in N/mm².

Q: Are there specific storage requirements for GB/T 802.3 nuts?
A: For uncoated carbon steel nuts, storage in dry conditions with controlled humidity is recommended to prevent corrosion prior to installation. For coated nuts, storage should maintain coating integrity by avoiding abrasive contact, impacts, or prolonged UV exposure that may affect coating performance.

Q: What surface treatments are available for these nuts?
A: Surface treatments include zinc plating (with clear, yellow, black, or olive drab chromate), zinc flake coating (Dacromet), nickel plating, chrome plating, phosphate coating, and other specialized coatings. Treatment selection is based on corrosion resistance requirements, appearance specifications, and environmental exposure conditions.

Installation Considerations
Pre-weld surface preparation should include removal of oil, grease, and oxide layers from the nut flange contact area and the workpiece surface to support weld consistency. Electrode force and welding current settings require calibration according to nut projection dimensions and material thickness. Post-weld inspection should verify fusion quality through visual examination and, where specified, through torque application tests. For plated or coated nuts, surface treatment application is typically performed after welding, unless welding is specified to occur prior to coating for corrosion protection of the weld zone.

When storing nuts prior to welding, the projection features should be protected from damage that could affect weld formation. Flange surfaces should remain free from contamination that would affect electrode contact and current flow during welding.