Product Overview This product is a custom-manufactured square head bolt / T-head bolt / clamp bolt, produced to GB/T 35 (Small Square Head Bolts) and related standards. It is designed for high-strength clamping, fixing, and positioning applications in machinery, railway, and heavy equipment. Available in carbon steel (Q235, 35#, 45#) and stainless steel (SUS304, SUS201, SUS316), with strength grades from 4.8 to 12.9, and surface finishes including black oxide, zinc plating, and plain. Product Type & Design Feature Description Product Type Square Head Bolt / T-Head Bolt / Clamp Bolt / Pressing Plate Bolt Head Type Square head (four-sided) or T-shaped head Standard GB/T 35-2013 (Small Square Head Bolts) / GB37 (T-slot bolts) / Non-standard custom Thread Type Metric coarse or fine thread; customized per drawing Thread Tolerance 6g The square head design allows the bolt head to be gripped securely with a wrench from four sides and prevents rotation when the bolt is seated in a square or T-slot recess — making it ideal for clamping and pressing applications where the bolt must remain fixed while the nut is tightened. GB/T 35-2013 specifies small square head bolts with thread sizes from M5 to M48, product grade B, and is the primary standard for this product category. GB37 covers T-slot bolts for machine tool tables and clamping fixtures. Material & Strength Grades Grade Material Tensile Strength (min.) Yield Strength (min.) Typical Applications 4.8 Low carbon steel (Q235) 400 MPa 320 MPa General clamping, light fixtures 8.8 Medium carbon steel (45#) 800 MPa 640 MPa Machine tool clamping, structural connections 10.9 Alloy steel (35CrMo/40Cr) 1,040 MPa 940 MPa Heavy machinery, railway, high-load fixtures 12.9 Alloy steel 1,220 MPa 1,100 MPa Critical high-strength clamping A2-70 Stainless steel SUS304 700 MPa 450 MPa Corrosion-resistant clamping, food machinery A4-70 Stainless steel SUS316 700 MPa 450 MPa Marine, chemical, high-corrosion environments Material options include carbon steel (Q235, 35#, 45#) for general industrial use, and stainless steel (SUS304, SUS201, SUS316) for corrosion-resistant applications. For SUS316 (S31635), typical mechanical properties include tensile strength ≥530 MPa, yield strength ≥205 MPa, and elongation ≥40%. Surface Finish Options Finish Coating Thickness Salt Spray Resistance Recommended Environment Black Oxide 1–2 μm 24–48 hours Indoor, machinery, tooling Zinc Plated 8–12 μm 72–144 hours General industrial, indoor/outdoor Plain (Machined) — 24–48 hours Temporary, indoor Heat Treated — — High-strength applications (10.9/12.9) For high-strength grades (10.9 and 12.9), heat treatment is required to achieve the specified mechanical properties. Zinc plating provides sacrificial corrosion protection for carbon steel bolts in moderate environments. Applications Square head and T-head bolts are widely used in: Machine tool clamping — T-slot bolts for securing workpieces and fixtures on machine tables Railway track fastening — Rail clamp bolts, pressure plate bolts, and track fixing Heavy machinery assembly — Equipment anchoring and structural connections Steel structure connections — Column base fixing and bracing Pressing plate systems — Clamping plates in industrial fixtures and jigs Mining and construction equipment — High-strength clamping in harsh conditions Food and chemical machinery — Stainless steel T-bolts for corrosion resistance The square head design is particularly suited for recessed slot applications where the bolt head must engage a T-slot or square pocket to prevent rotation during tightening. Customization & Manufacturing This is a factory-custom product — the manufacturer specializes in producing non-standard and customized fasteners to customer drawings or samples. Quality Assurance All products are manufactured under strict quality control procedures in accordance with GB/T 35-2013 and related standards. The product has achieved a 100% positive review rate with a 50% repurchase rate on the platform. Material test certificates (EN 10204 3.1), dimensional inspection reports, and third-party inspection reports (SGS, BV, etc.) can be provided upon request. For high-strength grades (8.8 and above), hardness testing and tensile testing are performed on each production batch.