Thread and bolt size chart.

A metric bolt is named by its nominal diameter in millimetres: M12 means 12 mm. ISO 261 gives each size one coarse pitch (M12: 1.75 mm) and finer options. The tables give pitch, diameters, stress area, tap drill, clearance hole and spanner size for each size.

Reviewed 11 Nov 2026 · Based on ISO 261:1998 ISO general purpose metric screw threads — General plan; ISO 724:1993 Basic dimensions; ISO 898-1:2013 (stress area formula); ASME B1.1-2019 Unified inch screw threads; ISO 273:1979 Fasteners — Clearance holes for bolts and screws · Report an error

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Metric coarse thread, ISO 261. Pick a size to see its key dimensions; the full tables follow below.

M12 × 1.75coarse pitch, mm
Fine pitches
1.5, 1.25 mm
Pitch diameter d2
10.863 mm
Minor diameter d3
9.853 mm
Stress area As
84.3 mm²
Tap drill (typical)
10.3 mm
Clearance hole f / m / c
13 / 13.5 / 14.5 mm
Spanner, ISO / DIN
18 / 19 mm

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Metric threads, M3 to M64
SizeCoarse pitch PFine pitchesPitch dia. d2Minor dia. d3Stress area As (mm²)Tap drill (typical)
M30.50.352.6752.3875.02.5
M40.70.53.5453.1418.83.3
M50.80.54.4804.01914.24.2
M610.755.3504.77320.15.0
M81.251, 0.757.1886.46636.66.8
M101.51.25, 19.0268.16058.08.5
M121.751.5, 1.2510.8639.85384.310.3
M1421.512.70111.546115.412.0
M1621.514.70113.546156.714.0
M182.52, 1.516.37614.933192.515.5
M202.52, 1.518.37616.933244.817.5
M222.52, 1.520.37618.933303.419.5
M243222.05120.319352.521.0
M273225.05123.319459.424.0
M303.5227.72725.706560.626.5
M333.5230.72728.706693.629.5
M364333.40231.093816.732.0
M424.5339.07736.4791,120.937.5
M485344.75241.8661,473.143.0
M565.5452.42849.2522,030.050.5
M646460.10356.6392,676.058.0
Source: ISO 261 (pitches), ISO 724 (d2, d3), ISO 898-1 (As = π/4 · (d − 0.9382 P)²). Tap drill = d − P, a workshop rule.
Clearance holes and spanner sizes (mm)
SizeFineMediumCoarseSpanner ISOSpanner DIN
M33.23.43.65.55.5
M44.34.54.877
M55.35.55.888
M66.46.671010
M88.49101313
M1010.511121617
M121313.514.51819
M141515.516.52122
M161717.518.52424
M18192021––
M202122243030
M222324263432
M242526283636
M272830324141
M303133354646
M33343638––
M363739425555
M42434548––
M48505256––
M56586266––
M64667074––
Source: ISO 273 clearance hole series; across-flats from ISO 4017/4032 and DIN 933/934.
Unified inch threads (UNC / UNF)
Size (in)UNC threads per inchUNC stress area (in²)UNC tap drillUNF threads per inchUNF stress area (in²)
1/4200.0318#7 (0.201 in)280.0364
5/16180.0524F (0.257 in)240.0581
3/8160.07755/16 (0.3125 in)240.0878
7/16140.1063U (0.368 in)200.1187
1/2130.141927/64 (0.4219 in)200.1600
9/16120.181931/64 (0.4844 in)180.2030
5/8110.226017/32 (0.5313 in)180.2560
3/4100.334521/32 (0.6563 in)160.3730
7/890.461749/64 (0.7656 in)140.5095
180.60577/8 (0.875 in)120.6630
1-1/870.763363/64 (0.9844 in)120.8557
1-1/470.96911-7/64 (1.1094 in)121.0729
1-1/261.40531-11/32 (1.3438 in)121.5810
Source: ASME B1.1 (As = 0.7854 · (d − 0.9743/n)²). Tap drills are common shop practice for about 75% thread.

Reference values, not a design.

Values are the nominal figures of the cited standards, or calculated from them where marked. The governing standard and your drawing always take precedence.

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Questions buyers ask.

What is the thread pitch of an M12 bolt?

The coarse pitch of M12 is 1.75 mm (ISO 261). Fine pitches of 1.5 mm and 1.25 mm are also standard. Unless a drawing says otherwise, M12 means the coarse pitch.

What size hole does an M10 bolt need?

ISO 273 gives three clearance hole sizes for M10: 10.5 mm fine, 11 mm medium and 12 mm coarse. Medium is the usual choice for general steelwork.

Why do DIN and ISO spanner sizes differ?

When DIN 933 and DIN 934 were replaced by ISO 4017 and ISO 4032, the across-flats size changed for M10 (17 to 16 mm), M12 (19 to 18 mm), M14 (22 to 21 mm) and M22 (32 to 34 mm). Other sizes stayed the same.

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