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Fastener Dimensions

Standard Dimensions for Bolts, Nuts, Washers & Fasteners

Metric Hex Bolt Dimensions (ISO 4014 / DIN 931)

Nominal Size (d) Width Across Flats (s) Width Across Corners (e min) Head Height (k) Thread Length
M6 10 mm 11.05 mm 4 mm 18 mm
M8 13 mm 14.38 mm 5.3 mm 22 mm
M10 16 mm 17.77 mm 6.4 mm 26 mm
M12 18 mm 20.03 mm 7.5 mm 30 mm
M16 24 mm 26.75 mm 10 mm 38 mm
M20 30 mm 33.53 mm 12.5 mm 46 mm
M24 36 mm 40.32 mm 15 mm 54 mm
M30 46 mm 51.28 mm 18.7 mm 66 mm
M36 55 mm 61.24 mm 22.5 mm 78 mm

Hex Nut Dimensions (ISO 4032 / DIN 934)

Thread Size Width Across Flats (s) Width Across Corners (e min) Nut Thickness (m) Washer Face Thickness
M6 10 mm 11.05 mm 5 mm 0.5 mm
M8 13 mm 14.38 mm 6.5 mm 0.6 mm
M10 16 mm 17.77 mm 8 mm 0.8 mm
M12 18 mm 20.03 mm 10 mm 1.0 mm
M16 24 mm 26.75 mm 13 mm 1.2 mm
M20 30 mm 33.53 mm 16 mm 1.5 mm
M24 36 mm 40.32 mm 19 mm 1.8 mm
M30 46 mm 51.28 mm 24 mm 2.0 mm

Plain Washer Dimensions (ISO 7089)

Bolt Size Inside Diameter (d1) Outside Diameter (d2) Thickness (h) Type
M6 6.4 mm 12.5 mm 1.6 mm Form A - Normal
M8 8.4 mm 16 mm 1.6 mm Form A - Normal
M10 10.5 mm 20 mm 2 mm Form A - Normal
M12 13 mm 24 mm 2.5 mm Form A - Normal
M16 17 mm 30 mm 3 mm Form A - Normal
M20 21 mm 37 mm 3 mm Form A - Normal
M24 25 mm 44 mm 4 mm Form A - Normal

Imperial Hex Bolt Dimensions (ANSI B18.2.1)

Nominal Size Width Across Flats Width Across Corners Head Height Thread Length
1/4" 7/16" 0.505" 11/64" 0.75"
5/16" 1/2" 0.577" 13/64" 0.875"
3/8" 9/16" 0.650" 1/4" 1.0"
1/2" 3/4" 0.866" 11/32" 1.125"
5/8" 15/16" 1.083" 27/64" 1.25"
3/4" 1-1/8" 1.299" 1/2" 1.375"
1" 1-1/2" 1.732" 21/32" 1.625"

Dimensional Tolerances

Metric Bolts (ISO 4759-1):

  • Width across flats: Class A = ±0.3mm (M6-M10), ±0.4mm (M12-M16)
  • Head height: ±0.2mm to ±0.5mm depending on size
  • Thread length: -0, +2P (P = thread pitch)

Imperial Bolts (ASME B18.2.1):

  • Width across flats: -0.015" to -0.045" depending on size
  • Head height: ±0.005" to ±0.015"
  • Thread length: As specified per ASME B18.2.1 Table 3