#4 Nut Dimensions & Size

#4 hex nuts are commonly used with #4 machine screws and bolts or threaded rods in light-duty mechanical assemblies, electronics, small appliances, sheet-metal connections, and precision hardware applications. They are designed to secure mating fasteners by providing internal threads that clamp components together when tightened against a surface or washer. Depending on the threads per inch (TPI), a #4 hex nut may be specified as a #4-40 nut for coarse-thread applications or a #4-48 nut for fine-thread assemblies where improved holding strength or increased vibration resistance is required. While the TPI differs, the external hex dimensions—such as width across flats and thickness—are standardized for compatibility with common miniature wrench sizes.

Disclaimer: Hex nut dimensions and tolerances may vary slightly by thread series (UNC or UNF), manufacturer, material, finish, or strength grade. Always verify critical dimensions using the official manufacturer product datasheet before installation.

Hex nut diagram showing diameter, width across flats, width across corners, thickness, and wrench size
#4 Hex Nut Dimensions – ANSI/ASME B18.2.2
Dimension Nominal Size Actual Size (in)
Min Max
Diameter #4 0.1061 0.1120
Width Across Flats 3/16 0.180 0.188
Width Across Corners Not specified 0.205 0.217
Thickness Not specified 0.057 0.066
Wrench Size 3/16 Not specified Not specified
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Frequently Asked Questions

What standard governs #4 hex nuts?

#4 hex nuts in the United States are typically manufactured to the ANSI/ASME B18.2.2 standard, which defines the external dimensions, tolerances, and geometry for inch-series hex nuts.

What bolt or screw size fits a #4 hex nut?

A #4 hex nut is designed to fit #4 machine screws, bolts, or threaded rods, most commonly #4-40 (UNC) and #4-48 (UNF) thread sizes.

What does “#4” mean on a hex nut?

“#4” refers to the nominal screw size of the mating fastener, not the wrench size or the nut’s external hex dimensions.

Are all #4 hex nuts the same?

No. While the external hex dimensions are standardized, differences can occur in threads per inch (#4-40 vs #4-48), material, finish, strength grade, and manufacturer tolerances.

What is ANSI/ASME B18.2.2?

ANSI/ASME B18.2.2 is the American standard that defines the dimensional requirements, tolerances, and geometry for inch-series hex nuts, including finished hex nuts and heavy hex nuts. It ensures that nuts from different manufacturers remain interchangeable and compatible with standard tools and mating fasteners.