Hex Nuts, Jam Nuts and Heavy Hex Nuts

ASME B18.2.2 · hex, jam and heavy hex nuts

What it is

FIELD IDENTIFICATION

Nut style is geometry: a hex nut is standard, a jam nut is thinner, and a heavy hex nut is wider across

flats and taller. Style does not set strength; the grade does.

HEX

JAM

HEAVY HEX

Jam nut is thinner; heavy hex is larger across

flats

Nominal dimensions, in

Size

Hex: across flats

Hex: thickness

Heavy hex: across flats

Heavy hex: thickness

1/4

7/16

7/32

1/2

15/64

5/16

1/2

17/64

9/16

19/64

3/8

9/16

21/64

11/16

23/64

7/16

11/16

3/8

3/4

27/64

1/2

3/4

7/16

7/8

31/64

5/8

15/16

35/64

1-1/16

39/64

3/4

1-1/8

41/64

1-1/4

47/64

7/8

1-5/16

3/4

1-7/16

55/64

1

1-1/2

55/64

1-5/8

63/64

Jam nuts use the hex across-flats size with reduced thickness.

Key points

A heavy hex Grade 2 nut is still Grade 2.

Structural bolts use heavy hex nuts to ASTM A563.

Governing standards: ASME B18.2.2-2022. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always take precedence over

this sheet.

torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability

arising from reliance on this reference.