Carbon and Alloy Steel Fastener Product Series

Carbon and alloy steels are the workhorses of industrial fasteners—bolts, screws, nuts, washers and studs—selected by strength grade and finish for different service conditions. The series spans plain grade 4.8 to high-strength 12.9 for machinery, steel structures, vehicles, tooling and general assembly as the foundation of structural and functional joints.

Selection weighs grade, material and finish by location, load and environment to avoid connection failure.

Strength Grade System

Per GB/T 3098.1, bolt grades are expressed as property classes: 4.8 for light joints, 8.8 as the common structural grade, 10.9 for higher preload and 12.9 for high-stress structures, achieved by material and heat treatment.

Grade follows design calculations and must be marked on drawings; substituting lower grades creates safety risk. Tensile and yield differ by grade—verify parameters before use.

Nuts and washers must match bolt grade—e.g. grade 8.8 bolts with grade 8 nuts—for coordinated thread engagement and load capacity.

Common Materials

Low-carbon steels (SWRCH22A, 1010) serve grade 4.8 and general self-tapping screws by cold heading, low-cost and ductile for light joints; medium-carbon steels (45#, SCM435) reach 8.8+ after quench and tempering, most widely used.

Alloy SCM435 reliably delivers 10.9 and 12.9 through controlled quenching and tempering for engines, hydraulics and heavy machinery. Material choice also weighs temperature, corrosion and cost; stainless or special alloys serve hot or corrosive sites.

Product Types

The range includes hex bolts, socket cap screws, flange bolts, double-end studs, hex nuts, flange nuts, flat washers, spring washers and self-tapping screws, from M3 to M36 plus imperial, with standard or drawing lengths.

Socket cap and socket-hex screws suit tight spaces with high torque and small heads; double-end studs serve flange joints and double-nut locking. Flange bolts replace bolt-plus-washer combos, simplifying assembly.

Finish Options

Zinc (clear, color, black) suits indoor general use; phosphating and blackening control friction; dacromet is hydrogen-safe for outdoor and high-strength joints; nickel and tin serve conductivity or appearance.

Grade 10.9+ plated parts carry hydrogen-embrittlement risk—control de-embrittlement or use dacromet/mechanical zinc for critical applications to reduce delayed fracture.

Inspection and Support

Each batch is checked for dimensions, threads, hardness, tensile and finish, with material certificates and reports; third-party verification is available for projects and export.

The platform supports drawing customization, stock on common sizes and batch supply, with selection advice and samples. Contact us for help.