ASME B18.2.6M Metric Heavy Hex Nuts for Structural Bolts (ASTM A563M)
ASME B18.2.6M-2012 metric heavy hex nuts for use with heavy hex structural bolts, ASTM A563M grades, M12 to M36: thread pitch, width across flats and corners, and thickness max/min — the structural mating nut ladder.
Last updated: 2026-11
Specifications
The heavy hex structural bolt is only half the connection — the mating nut is its own standard, B18.2.6M-2012, with geometry sized to develop the bolt's full strength in the ASTM A563M grades. The collected table runs M12 to M36 in the eight structural sizes: thread pitch 1.75 at M12 stepping to 4.0 at M36, width across flats s max/min (21/20.16 at M12 through 60/58.8 at M36), across-corners e max/min (24.25/22.78 at M12 to 69.28/66.44 at M36), and nut thickness m max/min (12.3/11.9 at M12 climbing to 36.6/35.0 at M36) — the depth that distinguishes a structural heavy nut from an ordinary heavy hex nut of the same across-flats. Against the registered B18.2.4.6M heavy hex nut page this identity is the structural series: same wrench sizes at the common diameters, thicker m, and A563M grade compatibility requirements instead of general property classes.
| Standard / scope | ASME B18.2.6M-2012 metric heavy hex nuts for use with heavy hex structural bolts (ASTM A563M) — M12, M16, M20, M22, M24, M27, M30, M36 |
|---|---|
| Thread pitch P | 1.75 (M12), 2.0 (M16), 2.5 (M20/M22), 3.0 (M24/M27), 3.5 (M30), 4.0 (M36) |
| Width across flats s | Max/min: 21/20.16 (M12) to 60/58.8 (M36) |
| Width across corners e | Max/min: 24.25/22.78 (M12) to 69.28/66.44 (M36) |
| Thickness m | Max/min: 12.3/11.9 (M12), 17.1/16.4 (M16), 20.7/19.4 (M20), 23.6/22.3 (M22), 24.2/22.9 (M24), 27.6/26.3 (M27), 30.7/29.1 (M30), 36.6/35.0 (M36) |
| Not tabulated | A563M grade/property requirements, proof-load testing, finishes (the coordinating bolt standard forbids galvanizing on A490M-class systems) — per RFQ |
Materials
- Structural nut supply is A563M grade-matched to the bolt system: pairing grade and proof-load requirements live in the ASTM standards, not in this geometry table. Supply with hot-dip galvanized A325M bolts needs a galvanized (overtapped per the system) nut; bare A490M systems take bare nuts. State the bolt system — not just "heavy hex nut M24" — on the RFQ, because the across-flats match the general heavy hex nut while the required performance does not
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 (ASME B18.2.6M Metric Heavy Hex Nuts for Structural Bolts (ASTM A563M)) 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 10,000 pieces. Stock items run 3–7 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
Why a separate structural nut standard when B18.2.4.6M heavy hex nuts share the same wrench sizes?
Because the structural connection loads the nut to the bolt's full ultimate: B18.2.6M nuts are thicker (m 24.2 at M24 vs the B18.2.4.6M heavy hex nut's shallower ladder), made to A563M grade requirements and proof-load tested as a system with the structural bolt. A general heavy hex nut of the same size may thread on and look identical, but it is not the certified half of a structural connection. For building and bridge work the nut is specified by the connection standard — order "B18.2.6M structural nuts, A563M grade per the bolt system", and the geometry table on this page is the supply check, not the spec basis.
What does the m max/min thickness band mean on site?
It is the acceptance band: every delivered nut's measured thickness must fall between the max and min values (e.g. 24.2/22.9 at M24). The min matters most — nut stripping strength in the structural system is a function of thread engagement depth, so an under-thickness nut fails the system even if it torques up fine. Receiving inspection that checks m against this ladder (plus across-flats against s) is cheap insurance on a connection whose paperwork will be audited; the values here are the geometry check, with the A563M certificate carrying the material side.
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