Stainless Steel Heavy Hex Nuts

What is a heavy hex nut & when to use it?

A heavy hex nut has:

Larger across-flats size than a standard hex nut

Greater thickness (height)

Use a heavy hex nut when you need:

Higher clamp load / stronger joints

More bearing surface under the nut (spreads load better)

Structural / critical applications (steel structures, flanges, high-strength bolted joints)

Typical uses:

Structural steel connections (beams, columns, bracings)

Flange connections in piping / equipment

High-strength bolt assemblies where standard nuts are not sufficient

Environment & corrosion

For stainless versions (if you’re supplying stainless heavy hex nuts):

Indoors / general outdoor → A2 (304) heavy hex nut

Marine / coastal / chemical / chloride exposure → A4 (316) heavy hex nut

Match nut material with the bolt material:

A2 heavy hex nut with A2 bolts

A4 heavy hex nut with A4 bolts

For carbon steel structural systems, heavy hex nuts are usually matched to bolt grade & coating (plain, zinc, HDG, etc.).

Strength & matching with bolt grade

Heavy hex nuts are chosen primarily for strength and bearing area.

For stainless systems:

With A2-70 / A4-70 bolts → use A2-70 / A4-70 heavy hex nuts

With higher-grade stainless bolts (e.g., A4-80) → use matching or higher-grade heavy hex nuts as specified

For carbon steel structural bolts (example: A325 / A490 type systems):

Use heavy hex nuts meeting the appropriate nut standard/property class specified for that bolt (e.g., structural nut grades).

Rule of thumb:

The heavy hex nut property class must be ≥ bolt property class, and must follow the same material family (stainless with stainless, structural carbon steel with structural bolts).

Application type: when heavy hex is preferred over standard hex

Choose a heavy hex nut instead of a standard hex nut when:

You need higher preloads (higher tightening torque)

The design requires greater safety factor against thread stripping / bearing failure

You’re following a structural or flange standard that calls for heavy hex nuts specifically

You want more wrenching surface and robustness in harsh assembly conditions

For light / medium-duty general-purpose joints, a standard hex nut is usually sufficient.

Heavy hex nuts are defined by their geometry (larger AF & height) and property class / grade.

Mechanically, their property class (e.g., A2-70, A4-70, structural nut grade) determines the proof strength and compatibility with the bolt.

Stainless heavy hex nuts – typical guide

A2-70 Heavy Hex Nuts

Material: A2 (304) stainless steel

Property class: 70

Intended for use with A2-70 bolts / studs

Suitable for general structural stainless joints, equipment frames, moderate outdoor environments.

A4-70 Heavy Hex Nuts

Material: A4 (316) stainless steel

Property class: 70

Intended for use with A4-70 bolts / studs

Suitable for marine, coastal, chemical, and chloride-rich environments where both strength and high corrosion resistance are required.

Higher class (e.g., A4-80) Heavy Hex Nuts (if used)

Used with A4-80 bolts in high-strength stainless joints

Provide higher proof load and allow higher clamp forces

Key mechanical points:

Higher proof strength vs. lower classes → allows higher tightening torque and clamp load.

Larger nut height → more thread engagement → improved resistance to thread stripping.

Larger across-flats → allows higher tool torque and better handling in heavy applications.