Interactive size finder
Find a Nut Size and Wrench Size
Select a known nut size or enter a measured width across flats. Measurements identify likely geometry—not thread compatibility or grade.
Identify a nut from a measurement
Closest listed regular hex nut
Enter a positive across-flats measurement to compare against the active U.S. or metric subset.
- D — nominal thread size
- 1/2 in
- s / F — across flats
- 3/4 in
- e / G — across corners
- —
- m / H — nut height
- 7/16 in
Scope warning
Regular hex-nut dimensions only. Heavy hex, jam, flange, prevailing-torque/lock, structural, coupling, machine-screw, legacy, and manufacturer-specific nuts can use different external dimensions. A wrench-size match does not prove thread pitch, grade, material, or product standard.
Reference table
Standard Hex Nut Size Chart
A deliberately limited common-size reference. U.S. and metric values stay tied to their native systems; metric ranges show source-controlled minimum/maximum geometry where available.
Use the system selector above to switch U.S. or metric rows. Search by nut designation, wrench size, standard, or dimension.
No regular hex nut matches the current search. Check the standard system, nut style, thread size, and measurement.
Scroll horizontally to view additional columns and vertically to view additional rows. Column headers remain visible while scrolling.
| Identification | External dimensions | Converted reference | Copy | ||||
|---|---|---|---|---|---|---|---|
| System / basis | |||||||
| 1/4 in | U.S. inch · ASME B18.2.2-2022 | 1/4 in | 7/16 in | — | 7/32 in | 11.11 mm AF; 5.56 mm high | |
| 5/16 in | U.S. inch · ASME B18.2.2-2022 | 5/16 in | 1/2 in | — | 17/64 in | 12.7 mm AF; 6.75 mm high | |
| 3/8 in | U.S. inch · ASME B18.2.2-2022 | 3/8 in | 9/16 in | — | 21/64 in | 14.29 mm AF; 8.33 mm high | |
| 7/16 in | U.S. inch · ASME B18.2.2-2022 | 7/16 in | 11/16 in | — | 3/8 in | 17.46 mm AF; 9.53 mm high | |
| 1/2 in | U.S. inch · ASME B18.2.2-2022 | 1/2 in | 3/4 in | — | 7/16 in | 19.05 mm AF; 11.11 mm high | |
| 5/8 in | U.S. inch · ASME B18.2.2-2022 | 5/8 in | 15/16 in | — | 35/64 in | 23.81 mm AF; 13.89 mm high | |
| 3/4 in | U.S. inch · ASME B18.2.2-2022 | 3/4 in | 1-1/8 in | — | 41/64 in | 28.57 mm AF; 16.27 mm high | |
| 7/8 in | U.S. inch · ASME B18.2.2-2022 | 7/8 in | 1-5/16 in | — | 3/4 in | 33.34 mm AF; 19.05 mm high | |
| 1 in | U.S. inch · ASME B18.2.2-2022 | 1 in | 1-1/2 in | — | 55/64 in | 38.1 mm AF; 21.83 mm high | |
| M5 | Metric · ISO 4032:2023 | M5 (5 mm) | 8 mm nominal (7.78–8 mm) | 8.79 mm min | 4.4–4.7 mm | 0.315 in AF; 0.185 in max high | |
| M6 | Metric · ISO 4032:2023 | M6 (6 mm) | 10 mm nominal (9.78–10 mm) | 11.05 mm min | 4.9–5.2 mm | 0.3937 in AF; 0.2047 in max high | |
| M8 | Metric · ISO 4032:2023 | M8 (8 mm) | 13 mm nominal (12.73–13 mm) | 14.38 mm min | 6.44–6.8 mm | 0.5118 in AF; 0.2677 in max high | |
| M10 | Metric · ISO 4032:2023 | M10 (10 mm) | 16 mm nominal (15.73–16 mm) | 17.77 mm min | 8.04–8.4 mm | 0.6299 in AF; 0.3307 in max high | |
| M12 | Metric · ISO 4032:2023 | M12 (12 mm) | 18 mm nominal (17.73–18 mm) | 20.03 mm min | 10.37–10.8 mm | 0.7087 in AF; 0.4252 in max high | |
| M16 | Metric · ISO 4032:2023 | M16 (16 mm) | 24 mm nominal (23.67–24 mm) | 26.75 mm min | 14.1–14.8 mm | 0.9449 in AF; 0.5827 in max high | |
| M20 | Metric · ISO 4032:2023 | M20 (20 mm) | 30 mm nominal (29.16–30 mm) | 32.95 mm min | 16.9–18 mm | 1.1811 in AF; 0.7087 in max high | |
Do not infer thread pitch, strength grade, material, nut style, or standard compliance from wrench size alone. An em dash means that dimension is not included in this limited source excerpt—not zero.
Nut Size vs. Wrench and Socket Size
The nominal nut designation describes the mating thread size; it does not describe the outside hex. A 1/2-inch U.S. regular hex nut in this reference uses a 3/4-inch wrench, while an ISO-style M10 nut in the metric subset uses a nominal 16 mm across-flats dimension.
- Thread size
- The internal thread designation that must match the bolt or stud.
- Across flats
- The distance between opposite flat faces. This controls the nominal wrench or socket size.
- Across corners
- The larger corner-to-corner envelope. It matters for clearance but should not be used to select a wrench.
Regular Hex Nuts vs. Heavy Hex, Jam, Flange and Lock Nuts
The same nominal thread can appear in nut styles with different widths and heights. A heavy-hex nut is intentionally larger across the flats; a jam nut is thinner; flange and prevailing-torque designs add geometry that this page does not model.
Field check: If the measured wrench size or height disagrees with the chart, first verify the nut style instead of forcing a match to the nearest regular-hex row.
How to Measure a Hex Nut
- Measure across opposite flats. Keep the caliper jaws square to the two flat faces. Do not measure corner to corner.
- Measure nut height. Measure the axial thickness from one bearing face to the opposite face.
- Identify the internal thread separately. Use a known mating fastener, thread gauge, or direct thread measurement; do not infer pitch from the outside hex.
- Confirm the nut style and standard. Use the dimensional match as an identification aid, then verify the governing product specification where fit or acceptance matters.
Common nut identification mistakes
- Using corner-to-corner width as the wrench size.
- Assuming the bolt diameter and wrench size are the same number.
- Treating a close metric and SAE wrench fit as proof that the threads are interchangeable.
- Ignoring coatings, wear, deformation, or a different nut style when field measurements are slightly off.
Nut Size Chart Examples
Example 1 — known 1/2-inch nut
Assumption: The hardware is a regular U.S. hex nut represented by the limited table.
Select 1/2 in. The listed across-flats dimension is 3/4 in, so a 3/4-inch wrench or socket is the nominal tool size. The listed height is 7/16 in.
Sanity check: A substantially larger hex may indicate a heavy-hex or another nut style; verify the thread and product standard before replacement.
Example 2 — measured 16 mm across flats
Assumption: The part appears to be a metric regular hex nut and the measurement is taken across opposite flats.
Enter 16 mm in reverse lookup with Metric selected. The closest exact listed candidate is M10 in this ISO 4032-aligned subset.
Sanity check: Measure or gauge the internal thread before calling the part M10; external hex width alone cannot prove pitch or standard.
U.S. vs. Metric Hex Nut Dimensions
U.S. inch regular nuts and ISO metric regular nuts belong to different dimensional systems. Keep each system in its native units for identification, then use the page’s unit conversion only as a secondary measurement aid.
Use the U.S. table when
- The thread designation is fractional inch.
- The assembly uses U.S. inch fasteners and tools.
- You are checking a common finished/regular hex-nut envelope.
Use the metric table when
- The thread designation is M-size.
- You need ISO-style regular-nut geometry.
- You want coarse-pitch reference values for the listed sizes.
Do not “convert” the designation
- M10 is not an inch nut simply because 10 mm has an inch equivalent.
- A close wrench fit does not make unlike threads compatible.
- Always preserve the original thread system.
Standards, Scope, and Data Rights
Dataset: NUT-REGHEX-v1.0 · limited common-size regular hex-nut reference · source checked August 16, 2026.
The dimensional standards remain controlling. This page intentionally publishes a limited, transformed educational subset rather than reproducing complete standards tables. Use the official standard or manufacturer documentation for acceptance, purchasing, and production-critical dimensions.
- ASME B18.2.2-2022 — Nuts for General ApplicationsControlling inch-series scope and dimensional standard family. ASME states that tabulated dimensions govern acceptance where questions arise.
- ISO 4032:2023 — Fasteners — Hexagon regular nuts (style 1)Controlling metric regular-nut scope: metric coarse-pitch thread M5 to M39, product grades A and B. ISO copyright terms prohibit unrestricted reproduction.
- Bolt Depot — US Nut Size TableAccessible cross-check used for the limited U.S. across-flats/wrench-size and hex-nut-height rows shown here.
- Bossard — Hex nuts type 1Commercial product documentation confirming the ISO 4032 regular-hex-nut family and technical-drawing context; ISO 4032:2023 remains controlling.
Dataset and Source-Check Details
- Publisher
- Turn2Engineering
- Dataset version
- NUT-REGHEX-v1.0
- Source checked
- August 16, 2026
- Page scope
- 9 common U.S. regular/finished hex sizes + 7 common metric ISO-style regular hex sizes
- Native units
- Inches for U.S.; millimeters for metric
- Conversion
- 1 in = 25.4 mm exactly; converted displays never drive matching
- Missing value
- — means not included in this limited source excerpt
- CSV rights decision
- Bulk and filtered standards-derived CSV disabled
- Maintenance trigger
- Re-check if ASME B18.2.2 or ISO 4032 is superseded or redistribution terms change
Nut Size Chart FAQ
The nominal wrench or socket size corresponds to the nut’s width across opposite flats for the applicable nut standard; it is not the same number as the nominal bolt diameter.
Measure across two opposite flats to identify the likely wrench-size family, then verify the internal thread diameter and pitch independently before naming or replacing the nut.
The nominal nut designation corresponds to the mating thread diameter, while the external hex and wrench size are separate, larger dimensions.
No. Similar outside dimensions do not establish compatible thread diameter, pitch, tolerance, or product standard.
It may be a heavy-hex, jam, flange, lock, structural, legacy, worn, coated, or manufacturer-specific nut rather than the regular-hex style covered by this page.
Nut Size Chart Summary
Use the nominal thread designation when you already know it, and use width across flats to choose the nominal wrench or socket. If you start from a field measurement, treat the reverse lookup as a candidate finder: confirm thread diameter, pitch, nut style, material/grade requirements, and the governing standard before substitution.