Hex High Nut Guide: Grades, Dimensions & Uses
A hex high nut — also called a high nut or thick nut — is a tall six-sided nut that runs roughly 30–45% thicker than a heavy hex nut of the same diameter. The extra height puts more threads in engagement, so the nut develops the full strength of a high-grade bolt or stud without stripping, and gives a wrench more surface to grip. High nuts are made to the dimensional requirements of SAE J482, with mechanical properties to SAE J995 for thick nuts. This guide covers what they are, the Grade 8 and Grade 5 strength levels, standard sizes and wrench dimensions, and where they get used.
What a High Nut Is (and Isn't)
A high nut looks like a tall hex nut. Its thickness is close to the bolt diameter, versus a finished hex nut at about seven-eighths of the diameter and a heavy hex nut somewhat more. That added length is the whole point: it holds more threads, so it can carry the tension a Grade 8 stud is capable of, and it protects the thread ends on all-thread and tie-rods. It is not a coupling nut. A coupling nut is longer still and is meant to join two lengths of threaded rod end to end — if you need to extend rod, see our Coupling Nut & Threaded Rod Guide. A high nut is a load-carrying nut, not a connector.
Grade 8 vs. Grade 5 High Nuts
High nuts are commonly stocked in two carbon-steel strength levels. Match the nut to the bolt grade so the nut is never the weak link — a Grade 8 stud wants a Grade 8 nut.
| Property | Grade 8 | Grade 5 |
|---|---|---|
| Material | Carbon steel | Carbon steel |
| Proof load, coarse (UNC) | 165,000 psi min | 133,000 psi min (up to 1"); 116,000 psi min (over 1") |
| Proof load, fine (UNF) | 150,000 psi min | 120,000 psi min (up to 1"); 105,000 psi min (over 1") |
| Hardness | Rc 24–32 (up to 5/8"); Rc 26–34 (3/4" to 1"); Rc 26–36 (1-1/4" to 1-1/2") | Rc 32 max |
Mechanical properties per SAE J995 for thick nuts. Most of our high-nut stock is Grade 8; ask us if you need a specific grade, thread, or finish.
For the full bolt-to-nut grade picture across inch and metric, see our Nut Grade & Bolt-Matching Guide.
High Nut Sizes & Wrench Dimensions
Standard SAE J482 high nuts use the same width across flats as a finished hex nut of the same diameter, so the wrench size is what you would already expect. The thickness is what sets them apart. Dimensions below are nominal per SAE J482; confirm against the specific part for a critical fit.
| Diameter | Width Across Flats (wrench) | Thickness (nom.) |
|---|---|---|
| 1/4" | 7/16" | 3/8" |
| 5/16" | 1/2" | 29/64" |
| 3/8" | 9/16" | 1/2" |
| 7/16" | 11/16" | 39/64" |
| 1/2" | 3/4" | 21/32" |
| 9/16" | 7/8" | 49/64" |
| 5/8" | 15/16" | 27/32" |
| 3/4" | 1-1/8" | 1" |
| 7/8" | 1-5/16" | 1-5/32" |
| 1" | 1-1/2" | 1-5/16" |
| 1-1/8" | 1-11/16" | 1-1/2" |
| 1-1/4" | 1-7/8" | 1-11/16" |
Dimensions nominal per SAE J482. Truck-suspension high nuts are sometimes made in special width-across-flats and thickness combinations that differ from this standard table — see the FAQ below.
Where High Nuts Are Used
High nuts show up wherever a joint needs full thread engagement, extra wrenching area, or a nut that can develop a high-grade stud's strength:
- Automotive and truck suspension — the biggest market; ground vehicles and heavy equipment that need extra wrenching area and durable, reusable joints.
- Tie-rods and all-thread — the tall body protects thread ends and keeps more threads in engagement under load.
- Leveling and jacking screws — the added length resists thread wear from repeated adjustment.
- Industrial equipment — anywhere a Grade 8 stud needs a nut that can carry its full rated tension.
Frequently Asked Questions
What is the difference between a high nut and a heavy hex nut?
Height. A high nut is roughly 30–45% thicker than a heavy hex nut of the same diameter. The extra length holds more threads, so the nut can develop the full strength of a high-grade bolt and protect thread ends, and it gives a wrench more surface. A heavy hex nut is wider across the flats than a finished hex nut but not as tall as a high nut.
What is the difference between a high nut and a coupling nut?
A high nut is a load-carrying nut sized to hold a bolt or stud with full thread engagement. A coupling nut is longer and made to join two lengths of threaded rod end to end. If you are extending or connecting rod, use a coupling nut, not a high nut.
What grade are high nuts?
Most are Grade 8 or Grade 5 carbon steel, with mechanical properties to SAE J995 for thick nuts. Grade 8 has a 165,000 psi minimum proof load on coarse thread; Grade 5 is 133,000 psi up to 1 inch. Match the nut grade to the bolt grade.
Why do I see two versions of the same size high nut, like 3/4-16?
Standard SAE J482 high nuts and truck-suspension high nuts can share a thread size but use different widths across the flats. A standard 3/4-16 high nut is 1-1/8 inch across the flats; a truck-suspension version can be 1-1/16 inch. Check the width across flats, not just the thread, so you order the right wrench size.
What wrench size does a high nut take?
The same as a finished hex nut of that diameter, since standard high nuts share the J482 width across flats. For example, a 1/2 inch high nut takes a 3/4 inch wrench, and a 3/4 inch high nut takes a 1-1/8 inch wrench.
Need High Nuts?
Grade 8 and Grade 5 hex high nuts in inch sizes, plain and plated, by the piece or in bulk.