ASME B18.2.2

Covers — dimensions and tolerances for inch-series nuts: hex, heavy hex, square, hex flange, coupling, and machine-screw nuts, including width across flats and thickness.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Nut material/strength grades → ASTM A194 / A563.
• Bolt/screw dimensions → ASME B18.2.1.
• Metric nut dimensions → ISO 4032; metric properties → ISO 898.

B18.2.2 gives the nut geometry; the grade (2H, etc.) is set by the A194/A563 material spec.

B18.2.2 sets minimum requirements for nut dimensions:

• Nut Types — hex, heavy hex, square, flange, and coupling nuts.
• Dimensions — width across flats/corners and nut thickness by nominal size.
• Tolerances — dimensional tolerances for wrench fit and thread engagement.

ASME B18.2.2 is the inch-series nut dimensional standard, defining across-flats sizes, thickness, and tolerances for hex, heavy-hex, square, flange, and coupling nuts. Heavy-hex nuts pair with heavy-hex bolts on pressure flange joints.

Like B18.2.1 for bolts, it governs geometry only — the nut grade (2H, 8, etc.) and strength come from ASTM A194 or A563. Nut thickness is not incidental: adequate thread engagement is what lets the joint reach full bolt load without stripping. Metric equivalent is ISO 4032.

Engineering Note: Match nut style and thickness to the bolt (heavy-hex nut on heavy-hex bolt) — a general-purpose thin nut on a high-strength flange stud can strip before the target preload is reached.