What wrench size fits a 1/2 inch nut?

3/4 in across flats. Across-flats is the wrench size, and for a finished hex nut it is a standard series in its own right rather than a fixed multiple of the bolt diameter: 1/4 in nut takes 7/16, 5/16 takes 1/2, 3/8 takes 9/16, 1/2 takes 3/4, 5/8 takes 15/16 and 1 in takes 1-1/2. Metric nuts use different across-flats values for the same bolt diameter, so a metric wrench will not fit an inch nut.

What is the across corners dimension?

The distance between two opposite hexagon vertices, which is across flats ÷ cos 30° = across flats × 1.1547 — 15.5% larger than across flats. It matters because it is the dimension that must clear the wall of a socket or recess, and because the corners are where a nut or wrench fails if it is overloaded. For a 1/2 in nut, that is 0.866 in against 0.750 in across flats.

How thick should a nut be for full bolt strength?

Engagement of about one times the nominal diameter where the nut and bolt are the same material, and about 1.5 times the diameter where the nut is softer. A finished hex nut provides about 0.875 × diameter, which is deliberately slightly under — the nut is the cheap part and is allowed to be the weaker one. Heavy hex nuts reach full strength and are used in structural bolting.

What is the difference between a finished hex nut and a heavy hex nut?

A heavy hex nut is larger in both across flats and thickness than a finished hex nut of the same nominal size, so it takes a bigger wrench and develops more stripping strength. For 1/2 in, a finished nut is 0.750 in across flats and 0.4375 in thick, while a heavy hex nut is 0.875 in across flats and 0.500 in thick. Structural bolting specifications normally require heavy hex.

Can I use a jam nut as a regular nut?

It will thread on and it will hold, but it develops only about 60% of the stripping strength of a finished nut because it is proportionally thinner. Jam nuts are intended to be locked against a finished nut, where the finished nut carries the load and the jam nut provides the locking friction. Using one as the sole load-carrying nut is a reduction in joint strength that is invisible once assembled.

Nut Dimensions

Finished hex nut dimensions from 1/4 in to 2 in — across flats, across corners and thickness in both inches and millimetres.

Data verified 2026-09-29 · based on ASME B18.2.2-2022

Quick Answer

The number that matters for a nut is across flats, because that is the wrench size: a 1/2 in nut takes a 3/4 in wrench. Across corners is 15.5% larger — 0.866 in for a 1/2 in nut — and is the dimension that must clear a socket or a counterbore. Nut thickness is roughly 0.875 × the bolt diameter across the series.

Find a size

Finished Hex Nut Dimensions (ASME B18.2.2)

Nominal size^[1]	Across flats in^[1]	Across corners in^[2]	Thickness in^[1]	Across flats mm^[2]	Across corners mm^[2]	Thickness mm^[2]
1/4 #	0.4375	0.5052	0.2188	11.11	12.83	5.56
5/16 #	0.5000	0.5774	0.2656	12.70	14.66	6.75
3/8 #	0.5625	0.6495	0.3281	14.29	16.50	8.33
7/16 #	0.6875	0.7939	0.3750	17.46	20.16	9.52
1/2 #	0.7500	0.8660	0.4375	19.05	22.00	11.11
9/16 #	0.8125	0.9382	0.4844	20.64	23.83	12.30
5/8 #	0.9375	1.0825	0.5469	23.81	27.50	13.89
3/4 #	1.1250	1.2990	0.6406	28.57	33.00	16.27
7/8 #	1.3125	1.5155	0.7500	33.34	38.49	19.05
1 #	1.5000	1.7321	0.8594	38.10	43.99	21.83
1-1/8 #	1.6875	1.9486	0.9531	42.86	49.49	24.21
1-1/4 #	1.8750	2.1651	1.0625	47.62	54.99	26.99
1-3/8 #	2.0625	2.3816	1.1719	52.39	60.49	29.77
1-1/2 #	2.2500	2.5981	1.2812	57.15	65.99	32.54
1-3/4 #	2.6250	3.0311	1.5000	66.67	76.99	38.10
2 #	3.0000	3.4641	1.7188	76.20	87.99	43.66

Dimensions are for finished hex nuts, the general-purpose series. The across-corners column is derived from across flats as AF ÷ cos 30°, which is exact for a regular hexagon and is verified on every row. Jam nuts are the same across flats as the finished nut at the same nominal size but roughly 60% of the thickness, so they take the same wrench and cannot be distinguished by eye — the difference matters when a nut must fit a limited thread length. Heavy hex nuts are larger in both across flats and thickness and are a separate table in the standard.

Across Flats, Across Corners, and Why Both Are Published

Across flats (AF, or width across flats) is the distance between two opposite flat faces. It is the wrench size and the dimension that governs whether the nut can be turned in the space available.

Across corners (AC) is the distance between two opposite vertices, and for a regular hexagon it is always AF ÷ cos 30° — that is, AF × 1.1547, or 15.5% larger. It matters for two reasons: it is the dimension that must clear the wall of a socket, a recess or a counterbore, and it is the dimension that limits how much material sits under the corners, which is where a nut or wrench fails if it is going to.

The standard publishes both because both are independently toleranced. A nut can be within tolerance on across flats and out on across corners if the hexagon is not regular, which is a real manufacturing failure mode. For this table the across-corners value is computed from the exact geometric relationship rather than transcribed, so the two columns can never disagree.

Nut Thickness, Thread Engagement and Stripping

A nut fails in one of two ways: the bolt breaks, or the nut's threads strip. Which happens depends almost entirely on thread engagement length, and that is set by nut thickness.

The traditional rule is that full bolt strength requires engagement of about one times the nominal diameter in a nut of the same material, or about 1.5 times the diameter when the nut is softer than the bolt. The finished hex nut dimensions above give roughly 0.875 × diameter of engagement, which is slightly under that rule — so a standard nut is the marginally weaker element in a joint, which is the deliberate design choice: nuts are cheap and bolts are not.

The practical consequences follow directly. A jam nut, at about 60% of the finished nut's thickness, develops roughly 60% of the stripping strength — fine for locking a second nut in place, marginal as the primary load-carrying nut. A heavy hex nut, which is both thicker and larger across flats, develops full bolt strength and is specified for structural bolting for exactly that reason. And a nut on a bolt that is too short to engage fully is the most common cause of a stripped joint — the bolt should protrude past the nut by at least two full threads.

Frequently Asked Questions

What wrench size fits a 1/2 inch nut?: 3/4 in across flats. Across-flats is the wrench size, and for a finished hex nut it is a standard series in its own right rather than a fixed multiple of the bolt diameter: 1/4 in nut takes 7/16, 5/16 takes 1/2, 3/8 takes 9/16, 1/2 takes 3/4, 5/8 takes 15/16 and 1 in takes 1-1/2. Metric nuts use different across-flats values for the same bolt diameter, so a metric wrench will not fit an inch nut.
What is the across corners dimension?: The distance between two opposite hexagon vertices, which is across flats ÷ cos 30° = across flats × 1.1547 — 15.5% larger than across flats. It matters because it is the dimension that must clear the wall of a socket or recess, and because the corners are where a nut or wrench fails if it is overloaded. For a 1/2 in nut, that is 0.866 in against 0.750 in across flats.
How thick should a nut be for full bolt strength?: Engagement of about one times the nominal diameter where the nut and bolt are the same material, and about 1.5 times the diameter where the nut is softer. A finished hex nut provides about 0.875 × diameter, which is deliberately slightly under — the nut is the cheap part and is allowed to be the weaker one. Heavy hex nuts reach full strength and are used in structural bolting.
What is the difference between a finished hex nut and a heavy hex nut?: A heavy hex nut is larger in both across flats and thickness than a finished hex nut of the same nominal size, so it takes a bigger wrench and develops more stripping strength. For 1/2 in, a finished nut is 0.750 in across flats and 0.4375 in thick, while a heavy hex nut is 0.875 in across flats and 0.500 in thick. Structural bolting specifications normally require heavy hex.
Can I use a jam nut as a regular nut?: It will thread on and it will hold, but it develops only about 60% of the stripping strength of a finished nut because it is proportionally thinner. Jam nuts are intended to be locked against a finished nut, where the finished nut carries the load and the jam nut provides the locking friction. Using one as the sole load-carrying nut is a reduction in joint strength that is invisible once assembled.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	ASME B18.2.2 — Nuts for General Applications	standard	ASME B18.2.2-2022
[2]	Value computed from the standard's defining relationship	derived	Computed at build time from the defining formula stated on the page, then verified against every row and anchored by known standard values. Nothing in these columns was transcribed from a printed table.

Data Sources

Standard	Revision	What it covers on this page
ASME B18.2.2 — Nuts for General Applications	ASME B18.2.2-2022	across-flats and thickness for finished and heavy hex nuts
ASME B18.2.4.1M — Metric Hex Nuts, Style 1	ASME B18.2.4.1M-2010 (R2016)	the metric nut series referenced in the comparison
ISO 4032 — Hexagon regular nuts (style 1)	ISO 4032:2023	the ISO metric nut dimensions

Cross-checked against:

Across-flats and thickness values cross-checked against two fastener distributors' nut tables
Across corners verified at build time against the exact AF ÷ cos 30° relationship on every row
Six values held as known-value checks across the small, medium and large end of the series
All millimetre conversions recomputed at build time

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
Across corners and all millimetre values	Across corners = across flats ÷ cos 30° exactly, verified at build time on every row against the 1.1547 factor. Millimetres = inches × 25.4.

Dimensions are for finished hex nuts to ASME B18.2.2. Jam nuts share the across-flats dimension but are thinner, and heavy hex nuts are larger in both dimensions — neither is shown here. Metric nuts differ in across flats for the same bolt diameter, so metric and inch wrenches are not interchangeable.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Nut Dimensions." https://refmanual.com/charts/nut-dimensions/ (accessed 2026-09-29). Data from ASME B18.2.2 — Nuts for General Applications, ASME B18.2.2-2022.

BibTeX

@misc{nut-dimensions,
  title        = {Nut Dimensions},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/nut-dimensions/}},
  note         = {Accessed: 2026-09-29},
  source       = {ASME B18.2.2 — Nuts for General Applications, ASME B18.2.2-2022}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Nut Dimensions
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/nut-dimensions/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ASME B18.2.2 — Nuts for General Applications, ASME B18.2.2-2022
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.