Dimensions of hex nuts, hex jam nuts, heavy hex nuts and heavy hex jam nuts are shown in the following charts according to ASME B18.2.2-1987 standard.

Hex nut is a hexagonal shape fastener which is used with a bolt to fix parts together. Hex jam nut is a type of nut with a thinner thickness with respect to a hex nut. Jam nut is generally used to lock a standard nut to prevent loosening and secure it in place.

Heavy hex nuts and heavy hex jam nuts are slightly thicker and larger than hex nuts and hex jam nuts. They are generally used for large diameter bolts. 

Some important notes from the ASME B18.2.2:

- The diameter range of hex nuts and hex jam nuts is from ¼ inch to 1 1/2 inches according to standard. For heavy hex nuts and heavy hex jam nuts, the range is from ¼ inch to 4 inches.

- Threads shall be Unified inch coarse, fine or 8 thread series with tolerance class of 2B (UNC, UNF, or UN-8).

- Unless otherwise specified, chemical and mechanical properties of steel nuts shall conform with ASTM A563 Grade A, Carbon and Alloy Steel Nuts; or Grade 2 of SAE J995, Mechanical and Material Requirements for Steel Nuts. Nuts of other materials such as stainless steel, brass, bronze, and aluminum alloys shall have properties as agreed upon between the manufacturer and purchaser. The properties for nuts of several grades of stainless steel alloys are covered in ASTM F 594, and of several nonferrous materials in the ASTM F 467.

- Hex nuts and hex jam nuts in sizes 5/8 in. (for heavy ones, this size is 7/16 in.) nominal size and smaller shall be double chamfered. Larger size nuts shall be double chamfered or have washer faced bearing surface and chamfered top.


Nominal diameter (inches)
Nut Type 


Dimensions of Hex Nut - Hex Jam Nuts
Parameter Symbol Value Unit
Product Name -- --- ---
Nominal Diameter d --- in
Width Across Flats [F] Fbasic ---
Fmax ---
Fmin ---
Width Across Corners [G] Gmax  ---
Gmin ---
Thickness Hex Nuts [H] Hbasic ---
Hmax ---
Hmin ---
Thickness Hex Jam Nuts [H1] H1_basic ---
H1_max ---
H1_min ---


Unified Screw Thread: A thread form used by the United Kingdom, Canada, and the United States to obtain screw thread interchangeability among these three nations. It has 60° thread angle and dimensions are stated in inch units.

UN form screw threads: The UN thread is intended for general purpose fastening operations.

UNC (Unified National Coarse): Most commonly used type for general engineering applications. This thread form is used in materials with low tensile strength which makes threads more resistance against stripping (internal threads) .UNC give possibility for quick assembly.

UNF (Unified National Fine): External threads of this Fine Series have greater tensile stress area than comparable sizes of the coarse series. The Fine series is suitable when the resistance to stripping of both external and mating internal threads equals or exceeds the tensile load carrying capacity of the externally threaded member. It is also used where the length of engagement is short, where a smaller lead angle is desired, where the wall thickness demands a fine pitch, or where finer adjustment is needed.

Thread class: A classification system to classify the threads for interchangeability and manufacturability. Class 1 threads are loosely fitting thread and used for ease of assembly. Most commonly used class is 2 and this class is designed for general use. Class 3 is used for closer tolerances.

Thread Gages and Gauging : Specifications and dimensions for the gages used on Unified inch screw thread is defined in the ANSI/ASME B1.2-1983 standard. Types of gages including thread plug gages, snap gages, thread ring gages and plain diameter gages for internal and external threads are covered in same standard. Screw thread gauging systems for acceptability is covered in the ASME B1.3-2007 standard.


Link Usage
Unified Inch Screw Thread Sizes & Tolerances Calculator Calculates basic major, minor and pitch diameters of the external (bolt) and internal (nut) inch thread according to ASME B1.1-2003 standard. In addition to basic size calculations, limits of sizes calculations of different tolerance classes can be done according to same standard.

  • Oberg.E , Jones.D.J., Holbrook L.H, Ryffel H.H., (2000) . Machinery's Handbook . 26th edition.  Industrial Press Inc.
  • ASME B18.2.2-1987, Square and Hex Nuts (Inch Series)