GB/T 5781-2025 Hexagon Head Bolts, Full Thread, Product Grade C
GB/T 5781-2025 fully threaded hexagon head bolts, product grade C, M5 to M64: pitch, runout, bearing face, across-flats and corners, head height and fillet ladders — the tolerance-loose general-construction full-thread bolt.
Last updated: 2026-11
Specifications
GB/T 5781 is the grade-C (rough tolerance) full-thread hex bolt — the construction-site bolt where holes are punched or drifted and the fastener geometry carries wider tolerances than the A/B grades. The collected 2025-edition table runs M5 to M64 across 24 sizes (non-preferred steps parenthesized as printed): pitch P from 0.8 at M5 to 6 at M64, thread runout a, bearing diameters dw and da, across-corners e min ladder (8.63 at M5 to 104.86 at M64 with the fine steps at the large end), head height k nominal 3.5 at M5 to 40 at M64 with min rows behind, fillet r, and across-flats s nominal 8 to 95 with its max/min ladder. A second corpus page carries the superseded GB/T 5781-2000 edition; this page renders the current 2025 edition and the 2000 file is pruned as same-identity-older-edition. Product grade C geometry pairs with the lower-tolerance end of the property-class ladder (typically 4.6-8.8 supply).
| Standard / scope | GB/T 5781-2025 hexagon head bolts, full thread, product grade C — M5 to M64, non-preferred sizes parenthesized as printed; 2025 edition (2000 edition pruned as older-edition duplicate) |
|---|---|
| Pitch P / runout a | P 0.8 (M5) to 6 (M64); a max 2.4 (M5) to 18 (M64) with the min sub-row behind it |
| Width across flats s | Nominal 8 (M5) to 95 (M64); min ladder 7.64 (M5) to 92.8 — max/min rows carried as printed |
| Width across corners e | Min ladder 8.63 (M5) to 104.86 (M64) with "-" sub-rows where not tabulated |
| Head height k / k w | k nominal 3.5 (M5) to 40 (M64), min 3.125 to 38.75; k w min 2.19 (M5) to 27.13 (M64); fillet r 0.2 to 2 |
| Not tabulated | Lengths, mechanical classes (grade C pairs with the coarse property classes), finishes — per RFQ |
Materials
- Grade C geometry is the Give on tolerance, not on material: supply is typically 4.6/4.8 carbon steel, hot-dip galvanized or black, for steel structures, temporary works and anchor bolting where drilled-fit precision is not the point. If the joint needs repeatable preload or a tight hole fit, that is an A/B-grade (GB/T 5783 / ISO 4017-family) conversation — say which on the RFQ, because the head sizes overlap and only the tolerance class differs on the certificate
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (GB/T 5781-2025 Hexagon Head Bolts, Full Thread, Product Grade C) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 1,000–10,000 pieces depending on size. Stock items run 3–7 days. High-strength and custom parts run 15–25 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
What does "product grade C" actually change versus the A/B hex bolts?
Tolerance, not strength or thread. Grade C bolts carry wider head and shank tolerances — they are built for punched, drifted or oversize holes in steel structures where the bolt must go in fast, not center precisely. The table shows it in the geometry's max/min spread and the "-" cells where tight-grade sub-rows simply are not tabulated. You trade repeatability for cost and speed of assembly; the property class stamped on the head still governs strength. Specifying C where the drawing says A (or vice versa) is a fitment problem waiting for the site — quote the product grade as printed.
Why does this page carry the 2025 edition when the corpus also collected a 2000 table?
The batch partition found both editions in the corpus and treats them as one identity with two editions: the page renders the current GB/T 5781-2025 ladder, and the 2000-edition file is pruned as a same-identity-older-edition duplicate rather than built as a competing page. Edition deltas at these sizes are minor geometry-detail shifts, but if a legacy drawing or an old certificate cites the 2000 values, flag it on the RFQ — the standard designation on the order should match the edition the design was verified against.
Related knowledge
- What Bolt Property Classes 8.8, 10.9 and 12.9 Encode — and When High Strength Stops Being the Right Choice
- Bolt Grade Selection: ISO 898-1 8.8/10.9/12.9 vs ASTM A307 and A325
- 8.8 vs 10.9 vs 12.9 Bolts: Strength, Hardness and Cost — What the Evidence Settles
- Calculating Bolt Preload and Clamp Force: Torque, Friction and Tightening Method
- How to Determine Tightening Torque and Choose a Tightening Method for a Bolted Joint
- Fastener Failure Modes: Which Fatigue, Creep and SCC Controls the Evidence Supports
- Hydrogen Embrittlement in High-Strength Bolts: Which Grades Need Controls, Which Coatings and Baking Schedules Are Acceptable, and What to Require Before the RFQ
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support