Nut dimension is the precise measured geometry of a nut as specified by a recognised engineering standard, e.g. ASME, DIN, ISO, BS or IS, the width across flats, the width across corners, and the thickness (or height), and the thread diameter. These are no frills numbers. The size of a nut across flats determines what spanner or socket can be used to install it at the job site, the number of threads it provides engagement to the mating bolt or stud, and whether or not it is able to seat properly and apply the specified gasket load to a flange joint. The nut might still thread on — until it strips, vibrates out of alignment, or fails to achieve proof load — if it is dimensioned incorrectly, or standards are mixed without verification.
Since 2014, Unifit Metalloys has produced Hex, Heavy Hex, Square and Lock nuts as per ASME, DIN, ISO, BS and IS dimensional standards in-house with an ISO 9001:2015 quality policy. The dimension tables, standard cross-references and designation rules that our engineering and quality staff use daily for metric and inch series and across the nut families that are most frequently used on piping, structural and flange drawings are compiled on this page. The data for the matching bolt and stud is found on our companion document of ASTM A193 GR.NB8 Bolts, within this page, nuts and bolts are specified on the same page.
All the nut dimensions on this page, and any page on a manufacturer's or standards body page, are based on the same four dimensions. One of the easier areas to get confused about when comparing DIN data with ASME or ISO data is that not all standards bodies use the same letter to refer to the same measurement. The following table illustrates the meaning of a parameter along with the letter that is often used to represent it.
| Parameter | What It Measures | Common Symbol |
|---|---|---|
| Nominal thread diameter | The major diameter of the internal thread — matches the mating bolt/stud size (e.g., M20, 3/4") | D |
| Width across flats | The distance between two parallel flat faces of the hex or square — the dimension a spanner or socket is sized to | F (also shown as W or S) |
| Width across corners | The distance between two opposite corners of the hex or square — governs minimum clearance in a housing or pocket | G (also shown as C or e) |
| Thickness/height | The overall height of the nut, measured face to face | H (also shown as M) |
In this example, a Hex Nut is specified by its dimensions.
A labelled cross section and top view of a standard hex nut with the height of the thread (D), width across the flats (F), width across the corners (G), and thickness (H), measured at the correct points.
The four parameters are sufficient to read any table on this page or a mill certificate, drawing callout or third-party datasheet; the tables that follow just populate D, F, G and H for a range of sizes for each nut type and standard.
Knowing which standard body has jurisdiction over which nut family (and where the jurisdictions overlap), helps with the extraction of numeric values. Procurement teams around the globe on an EPC job regularly encounter situations of needing to translate a DIN 934 hex nut callout to its ASME B18.2.2 equivalent, or simply determining if there is an IS or BS number available for a nut type. In this table, 10 families of nuts mostly used in industrial specifications are listed. Specific size charts along with the dimensions of hex, heavy hex, square and jam families of nuts are provided, while specifications for other nut families are also available on request based on the relevant standard and project specification.
| Product | DIN | ISO | ASME/ANSI | BS | IS | UNI | Measurement |
|---|---|---|---|---|---|---|---|
| Hex Nuts | 934 / 555 | 4032 / 4034 | B18.2.2 | 3692 / 4190 | 1364 | 82144 | Metric & Inch |
| Heavy Hex Nuts | 6915 | B18.2.2 (Heavy) | Metric & Inch | ||||
| Hex Jam / Thin Nuts | 439 / 936 | 4035 | B18.2.4.5M | 4190 | Metric | ||
| Hex Flange Nuts | 6923 | 4161 | B18.16.3M | Metric | |||
| Square Nuts | 557 / 928 | B18.2.2 | Metric & Inch | ||||
| Slotted / Castle Nuts | 935 | 7035 / 7038 | Metric | ||||
| Nylon Insert Lock Nuts (Nyloc) | 985 | 7040 | Metric & Inch | ||||
| Dome / Acorn Nuts | 1587 | 5721 | Metric | ||||
| Wing Nuts | 315 | 5448 | Metric | ||||
| Coupling Nuts | Metric & Inch |
The absence of a standard does not mean that the nut is not present in the market in question, but that the standards body in question does not have a separate standard for this nut. The absence of a standard does not indicate that the nut is not found in that market; generally, the buyer will state that they are interested in the nut and not indicate the exact standard, which they will probably find that they should look at the closest ASME/DIN equivalent.
Hex nuts under DIN 934 and ISO 4032 are dimensionally very similar over much of the metric range, and are often referred to jointly. The low-height version of the jam nut is covered by DIN 555. The values below are in millimetres; D, F and H are basic (nominal) values, and G is the maximum value.
| D (Thread) | F — Width Across Flats | G (max) — Width Across Corners | H — Thickness (DIN 934) |
|---|---|---|---|
| M3 | 5.5 | 6.35 | 2.4 |
| M4 | 7.0 | 8.08 | 3.2 |
| M5 | 8.0 | 9.24 | 4.7 |
| M6 | 10.0 | 11.55 | 5.2 |
| M8 | 13.0 | 15.01 | 6.8 |
| M10 | 16.0 | 18.48 | 8.4 |
| M12 | 18.0 | 20.78 | 10.8 |
| M16 | 24.0 | 27.71 | 14.8 |
| M20 | 30.0 | 34.64 | 18.0 |
| M24 | 36.0 | 41.57 | 21.5 |
| M30 | 46.0 | 53.12 | 25.6 |
| M36 | 55.0 | 63.51 | 31.0 |
| M42 | 65.0 | 75.06 | 34.0 |
| M48 | 75.0 | 86.60 | 38.0 |
The width across flats of DIN 555 hex jam nuts is the same as the DIN 934 size; only the thickness (H) is decreased, normally to 0.5D – 0.6D, depending on the nominal size.
ASME B18.2.2 is the standard that governs finished hex nuts of the inch series, which covers a range of sizes from 1/4" to 3". The basic values outlined below are usually used for the purpose of reference. However, maximum and minimum tolerance values should be confirmed based on the standard or the specification of the project involved.
| Nominal Size | F — Width Across Flats (Basic) | G — Width Across Corners (Basic) | H — Thickness (Basic) |
|---|---|---|---|
| 1/4" | 7/16" | 0.505" | 7/32" |
| 5/16" | 1/2" | 0.577" | 17/64" |
| 3/8" | 9/16" | 0.650" | 21/64" |
| 1/2" | 3/4" | 0.866" | 7/16" |
| 5/8" | 15/16" | 1.083" | 35/64" |
| 3/4" | 1-1/8" | 1.299" | 41/64" |
| 1" | 1-1/2" | 1.732" | 55/64" |
| 1-1/4" | 1-7/8" | 2.165" | 1-3/32" |
| 1-1/2" | 2-1/4" | 2.598" | 1-19/64" |
| 2" | 3" | 3.464" | 1-23/32" |
| 3" | 4-1/2" | 5.196" | 2-9/16" |
Inch hex nuts are furnished in the same mechanical grade as the bolts with which they are used; Grade 2, 5 and 8 nuts have the same dimension table, but the material and proof load requirements are found under the Nut Grades section below.
Heavy hex nuts (DIN 6915, ASME B18.2.2 Heavy Hex Series) have a wider bearing across flats and are thicker than a standard hex nut of the same nominal size, which results in a higher load capacity. This makes heavy hex the standard nut specified for ASME B16.5 flange bolting, and the same grade stud bolts as covered on our Flanges product range and described in more detail on the stud bolt section of the Bolts Dimension Standards page.
| Nominal Size | F — Width Across Flats | H — Thickness |
|---|---|---|
| 1/2" | 7/8" | 31/64" |
| 5/8" | 1-1/16" | 39/64" |
| 3/4" | 1-1/4" | 47/64" |
| 1" | 1-5/8" | 7/8" |
| 1-1/4" | 2" | 1-3/32" |
| 1-1/2" | 2-3/8" | 1-19/64" |
| 2" | 3" | 1-23/32" |
Hex jam nuts (DIN 439/936, ASME B18.2.4.5M) have the same width across flats as a standard hex nut but have a lower thickness and are generally used as a locking nut run down against a primary nut, or if space requirements prohibit the installation of a full-sized nut.
Where a flat instead of a round bearing face is required against timber, sheet metal or a slotted channel, or existing old structural and agricultural equipment which is still constructed according to the old drawings, square nuts with DIN 557 (and imperial equivalent ASME B18.2.2) are used.
| D (Thread) | F — Width Across Flats | G (max) — Width Across Corners | H — Thickness |
|---|---|---|---|
| M5 | 8.0 | 11.3 | 5.0 |
| M6 | 10.0 | 14.1 | 6.0 |
| M8 | 13.0 | 18.4 | 8.0 |
| M10 | 17.0 | 24.0 | 10.0 |
| M12 | 19.0 | 26.9 | 12.0 |
| M16 | 24.0 | 34.0 | 16.0 |
| M20 | 30.0 | 42.4 | 20.0 |
Nylon insert lock nuts (DIN 985 / ISO 7040) feature a nylon collar that is installed in the upper part of the nut to create a mechanical, non-spring washer, “thread-locking” action, which provides a resisting force in the form of prevailing torque when subjected to vibration. Outer dimensions (F, G) are equivalent to the standard hex nut in the same nominal size; additional features are the increased overall height (due to the nylon insert), and a lower proof load than an all-metal nut of the same grade, due to the fact that the nylon insert is part of the internal thread engagement. There are many places that these are specified, such as automotive assemblies, piping supports, and machinery mounts where there is repeated vibration or dynamic loading.
A complete nut designation is the designation that includes the standard, the nominal size and the material or mechanical grade, such as M20 – DIN 934 – Class 8 or 3/4"-10 UNC – Grade 8 Hex Nut. All of those parts of that string are important: the standard determines which dimensional table to use, the nominal size determines D and hence F and G and H (by lookup), and the grade determines the material and proof load the nut is rated to.
The designation should match the mating bolt or stud on the same drawing: A Class 8 nut is used with an 8.8 or higher bolt, and a Grade 8 nut is used with a Grade 8 bolt, so that the proof load of the nut is equal to or greater than that of the ultimate tensile capacity of the bolt. A very common failure mode and one that can be prevented is mismatching a lower-grade nut to a higher-grade bolt. Bolts and studs follow the same naming convention — our Bolts Dimension Standards page (How to Read a Bolt Size) gives the equivalent breakdown for the fastener side of the pair.
There are two types of Dimension standards, one that specifies the geometry of a nut, and another that specifies what it is made of and how much load it can withstand before failing. They are referred to together, but acted upon separately. ASTM A563 establishes a grade system (Grade 2, 5, 8 and their variants) for inch-series nuts, based on the above dimension tables for B18.2.2 nuts. ASTM A194 applies to nuts with high-temperature or pressure-retaining bolting, including grades 2H, 8 and 8M which match the corresponding studs from ASTM A193, B7, B8 and B8M. Nuts that conform with the DIN and ISO standards use reference classes of properties (Class 6, 8 and 10) according to ISO 898-2, which specifies minimum proof stress based on properties and not on the dimensional standard (F, G and H).
Full grade, chemistry and proof-load data is covered on our Bolts Dimension Standards page underBolt Grades, and on our individual material grade pages: Stainless Steel, Alloy Steel, Carbon Steel, Duplex Steel, Super Duplex Steel, Nickel Alloy, Monel, Hastelloy and Inconel.
The set of measurable values of geometry of a nut (nominal thread diameter (D), width across flats (F), width across corners (G), and thickness (H)) that are determined by a standard like ASME B18.2.2, DIN 934 or ISO 4032.
This is the standard height hex nut covered by DIN 934. The DIN 555 is a nut that has the same width across flats as a standard nut, but is thinner and is typically used as a jam or locking nut, not a load-bearing nut.
The width across flats of a hex or square nut is the distance between two flat faces that are parallel. It's the dimension a spanner, wrench or socket is sized against, and is denoted F (or W) on most dimension tables.
The major difference between a heavy hex nut and a standard hex nut is that the former has a larger width across flats and a larger thickness that provides a greater bearing area and load rating. Heavy hex nuts are the typical specification for flange bolting as per ASME B16.5.
The size of the nut used (nominal thread diameter, D) should be the same as the bolt, and the grade or property class of the nut should be equal to or greater than that of the bolt's mechanical grade; in this way, the proof load of the nut is not the weak point of the screw joint.
The standard is typically determined by the project specification, the area of installation or the existing standard for the mating bolt or stud. For inch-series work, ASME B18.2.2 is the default standard, and DIN 934 / ISO 4032 is the default for metric where there is flexibility in the project.
Wherever a joint is subjected to vibration or dynamic loading and is required to prevent self-loosening without a separate lock washer or thread locking compound, a Nyloc nut is used — the nylon insert mechanically locks the bolt thread by the prevailing torque it provides.
Since 2014, Unifit Metalloys has produced nuts according to ASME, DIN, ISO, BS and IS dimensional standards and has been producing them using an ISO 9001:2015 quality management system (QMS), with all products meeting the PED 97/23/EC and NACE MR0175 standards where applicable to sour-service applications. Hex, heavy hex, square and jam and lock nuts are stored in stock in both metric and inch sizes for speedy delivery to meet project deadlines. Comprehensive documentation is available for our Quality Policy and Certifications.
Looking for the right nut to fit a particular bolt or stud on your drawing? You can request a Quote, and our engineering team will verify your specification with the proper standard, grade and dimension.
Related: Fasteners Manufacturer in India | Flanges