ASME B18.2.4.6M-2010 — Metric Heavy Hex Nuts

28 10 月, 2026
ASME Standards

🔩 ASME B18.2.4.6M-2010 provides complete general and dimensional data for metric heavy hex nuts. Compared with regular hex nuts, heavy hex nuts have a larger width across flats, a larger circumscribed circle, and appropriately increased height, matching heavy hex bolts and structural bolts in high-load connections typified by steel construction, bridges, and heavy machinery. Revising ANSI B18.2.4.6M-1979 (R2003), the 2010 edition extends the size range to M12 through M100, coordinates dimensional differences as far as possible with ISO 4775, and was approved by ANSI on February 22, 2010.

💡 The most notable change in the 2010 edition is the greatly extended size range (to M100) and the coordination of dimensional differences with ISO 4775, presented in Nonmandatory Appendix A — letting U.S. and ISO heavy hex nuts interchange in global projects.

1. Scope 📌

This Standard covers the complete general and dimensional data for metric heavy hex nuts recognized as an American National Standard. Principal coverage includes:

Dimensions: the size range M12 through M100 in Table 1.
Width across flats: the heavy hex series, larger than regular hex nuts.
Thickness: coordinated with traditional heavy nuts to suit high-preload joints.
Tops and bearing surfaces, corner fill, true position, countersink, threads, material and mechanical properties, finish, identification symbols, inspection, and workmanship.

⚠️ Dimensional data do not imply that every M12–M100 size is a stock item. Confirm stock availability with manufacturers before purchasing to avoid schedule impact from less common sizes.

2. Coordination With ISO 4775 🌐

The 2010 revision coordinates dimensional differences as far as possible with ISO 4775 (high-strength structural-bolting nuts). Quality requirements include:

Stainless steel and nonferrous nuts conform to ASTM F 836M and are marked with property class and manufacturer per ASTM F 836M or ASTM F 467M.
Acceptability is determined per ASME B18.18.2 (its referenced inspection standard, current at time of order).
Workmanship references ASTM F 812/F 812M; symbols specifying geometric characteristics follow ASME Y14.5.
Nonmandatory Appendix A tabulates the dimensional differences between this Standard and ISO 4775; the former government-application Appendix 1 and Table 2 were removed.

Aspect	ASME B18.2.4.6M-2010	ISO 4775	Remark
Size range	M12–M100	M12–M36 (typical)	U.S. range is larger
Units	Millimeters (mm)	Millimeters (mm)	Metric system
Geometric symbols	ASME Y14.5	ISO tolerance symbols	Different symbol systems
Stainless requirements	ASTM F 836M	ISO 3506, etc.	Different references
Interchangeability	Differences per Appendix A		Good functional interchange

3. Key Geometry and Dimensions 🔧

Distinguishing features of the heavy hex nut:

Width across flats: one wrench size larger than the regular hex nut — verify tooling during design.
Thickness: adequate height to provide sufficient thread-shear area at high preload.
Tops and bearing surfaces: flat top with chamfered corners; flat bearing face perpendicular to the axis for even load transfer.
Threads: metric coarse (with fine in larger sizes), tolerance class typically 6H per the Standard.
Marking: property class and manufacturer per ASTM F 836M/F 467M for traceability.

🚨 Match the heavy hex nut’s property class to the bolt’s strength grade: never pair ordinary carbon-steel nuts with high-strength structural bolts in critical joints, or thread shear failure can result from insufficient nut strength.

4. Materials, Mechanical Properties, and Acceptance 📏

Steel: hardness and proof load per metric property classes (e.g., structural grades 8S, 10S); carbon and alloy steel nuts carry the manufacturer’s mark.
Stainless steel: conforms to ASTM F 836M, marked with property class (e.g., A4-80) and manufacturer.
Nonferrous metals: conform to ASTM F 467M, marked by material grade.
Acceptance: dimensions per Table 1, sampling per ASME B18.18.2, and thread gaging per the ASME B1.13M system.

5. Engineering Practice Essentials 🛠️

🔍 Selection workflow: determine bolt size and strength grade (e.g., grade 10.9 structural bolts) → select the matching heavy hex nut series → check width across flats, wrench size, and bearing area → specify material and finish.
🔧 Preload control: use the torque method, turn-of-nut, or direct tension indicators on site; the heavy hex nut provides ample bearing area for high preload.
📊 Washer selection: use hardened flat or beveled washers per ASTM F 436 to prevent bearing-surface indentation.
📋 Traceability: request material certificates and verify property-class markings; run proof-load tests per lot and keep records.

6. Frequently Asked Questions ❓

❓ Q: How do heavy hex nuts differ from regular hex nuts (Styles 1/2)?
A: Heavy hex nuts have a larger width across flats (one wrench size up), a larger circumscribed circle, and moderately greater height, designed for high-load structural connections; regular nuts serve general machinery joints.

❓ Q: Can nuts to this Standard interchange with ISO 4775 nuts?
A: Functional interchangeability is good at corresponding sizes, but verify each dimension against the Appendix A comparison table; stainless and nonferrous marking systems differ, so specify the acceptance standard in the order.

❓ Q: Are large sizes such as M100 common in practice?
A: M100 is an ultra-large size for giant structural nodes or heavy machinery; most projects use M12–M48. The extension provides a standard basis for special projects, not a promise of stock.

🔍 Q: Why was the government-application appendix removed in 2010?
A: As the metric fastener system and related national standards matured, the former part-numbering scheme was absorbed by standards such as ASME B18.24, and the appendix content was consolidated or superseded.