Hex Nut Dimensions & Wrench Size Chart — Metric & Inch

Hex nut dimension lookup

Search the chart by thread designation, then filter metric or inch rows. The lookup covers regular finished hex nuts in the ISO 4032:2023 metric style-1 family and the ASME B18.2.2-2022 inch finished-hex family. It shows width across flats, width across corners, nut thickness, and the matching wrench or socket size.

The chart uses one explicit nut style: regular. It does not combine regular nuts with jam nuts, heavy-hex nuts, lock nuts, flange nuts, coupling nuts, or other special families. A similar thread designation does not make those parts interchangeable.

What “across flats” means

Across flats is the distance between two opposite parallel faces of the hexagon. It is the dimension that a conventional open-end wrench, combination wrench, or six-point socket engages. That is why an M8 regular nut maps to a 13 mm wrench in this chart, while a 1/2-13 regular inch nut maps to a 3/4 in wrench.

Across flats is not the thread diameter. The M8 designation identifies the nominal mating thread; the 13 mm wrench size describes the outside hex. The same relationship applies to inch hardware: 1/2-13 means a nominal 1/2 in thread with 13 threads per inch, not a 1/2 in wrench size.

Across corners and socket clearance

Across corners is the largest ideal distance across the hex profile. For the regular-hex geometry used here, the chart calculates it from across flats:

across corners = across flats ÷ cos(30°)

This is a geometry result, not an additional standard tolerance. Chamfers, corner radii, manufacturing tolerances, and the actual socket opening can change the usable clearance. Use the calculated value for early envelope checks, then verify the exact nut and tool when a pocket, counterbore, or close wall controls the design.

Nut thickness is a separate dimension

Nut thickness is the axial height of the nut. It affects thread engagement, protruding thread length, clamp-stack height, and whether a standard socket can reach the flats. Do not infer thickness from the wrench size. An M12 regular nut is 18 mm across flats and 10 mm thick in this bounded ISO reference, while a 1/2-13 regular nut is 3/4 in across flats and 7/16 in thick in the bounded inch reference.

Jam nuts are intentionally thinner. Heavy-hex nuts are wider and thicker. Lock and flange nuts add different features and may require different tool or clearance dimensions. Select the matching family before using a nut in an assembly model or bill of materials.

Metric and inch rows

Metric rows use ISO 4032:2023 regular nuts, style 1, with coarse metric pitches such as M8 × 1.25 and M12 × 1.75. Inch rows use ASME B18.2.2-2022 finished hex nuts with UNC designations such as 1/4-20, 3/8-16, and 1/2-13. Metric and inch rows remain separate in the filter and in the source notes.

Inch-native values are preserved in inches and converted to millimeters for the canonical dataset. Converted values are convenience values, not independent standard limits. Keep the source-unit dimension and the governing family on a production drawing.

Regular hex versus heavy hex and jam nuts

A regular finished hex nut is the everyday nut family represented here. A heavy-hex nut has a larger across-flats dimension and a greater thickness for structural or high-load applications. A jam nut is thinner and is used where adjustment or locknut stacking requires less axial height. A prevailing-torque lock nut or flange nut has additional functional geometry.

Do not choose a heavy-hex nut because its thread matches a regular nut. Do not use a jam-nut thickness to calculate the engagement of a regular nut. If the purchase description includes “heavy hex,” “jam,” “nylon insert,” “all-metal lock,” “flange,” or “coupling,” leave this lookup and use that exact product standard.

How to use the dimensions in CAD

1. Read the complete thread designation and nut family from the drawing or purchase record.
2. Use the width across flats to select the wrench or socket.
3. Use nut thickness to check clamp-stack height and available thread engagement.
4. Use across corners for early pocket and wall-clearance checks.
5. Verify the exact standard, grade, coating, tolerance, and supplier drawing before release.

For the related bolt-to-tool lookup, use the bolt size to wrench and socket size chart. For the complete mating fastener envelope, compare the hex bolt dimensions chart. Thread pitch details are available in the metric thread pitch chart and the UNC and UNF thread chart.

Sources and limits

The metric scope follows ISO 4032:2023. The inch scope follows ASME B18.2.2-2022. The inch rows also use a Fastenal finished-hex product standard as a manufacturer cross-check. The complete standards are licensed, so this bounded dataset must be reconciled against the licensed row and the selected supplier before production use.

Frequently asked questions

What wrench fits an M8 hex nut?

The bounded ISO 4032 regular-nut row uses a 13 mm width across flats, so a 13 mm wrench or socket is the matching nominal tool size.

What wrench fits a 1/2-13 hex nut?

The bounded ASME B18.2.2 regular finished-hex row uses a 3/4 in width across flats, so a 3/4 in wrench or socket is the matching nominal tool size.

Is a heavy-hex nut the same as a regular hex nut?

No. Heavy-hex nuts are wider and thicker. Match the nut family to the standard and the drawing instead of selecting by thread alone.

Can I use across corners as the socket size?

No. A conventional wrench or socket engages across flats. Across corners is an outer-envelope dimension used for clearance checks.