Heavy Hex Nuts
What Are Heavy Hex Nuts?
Heavy hex nuts are thicker and wider versions of standard hex finish nuts. The larger width across flats and increased height provide a higher bearing surface and thread engagement for demanding joints. They are commonly paired with heavy hex bolts, structural bolts, carriage bolts, threaded rod, and anchors where added strength, durability, or a thicker finished appearance is required.
Why Choose Heavy Hex Nuts?
- Higher clamping force: Larger bearing face distributes load and resists embedment in soft or structural materials.
- More thread engagement: Increased nut height improves strength in high-load connections.
- Better tool access: Wider wrench flats provide secure socket/wrench bite under high torque.
- Standards-based: Available to ASME/ANSI and ASTM/SAE structural specs for predictable fit and torque.
Materials & Finishes
- 18-8 / 304 Stainless Steel: General corrosion resistance for indoor/outdoor use.
- 316 Stainless Steel: Superior resistance for marine, chemical, and chloride environments.
- Zinc Plated Carbon Steel: Economical protection for dry or sheltered areas; bright appearance.
- Hot-Dip Galvanized (HDG): Heavy zinc coating for exterior structural applications (use with HDG bolts/rods sized for coating).
- Plain / Phosphate Alloy Steel: High strength; protect after assembly when used in corrosive settings.
Common Applications for Heavy Hex Nuts
- Structural steel connections (bridges, buildings, support frames)
- Heavy equipment, off-road, and industrial machinery
- Anchor bolt terminations and embedded rod connections
- Pole bases, guardrails, racking, and infrastructure
- Marine and outdoor assemblies (use 316 SS or HDG)
How to Select the Right Heavy Hex Nut
- Match diameter & pitch: The nut must match the bolt/rod thread exactly (e.g., 3/4-10, 1-8, M20-2.5).
- Match strength: Select a nut grade or ASTM/ISO class that equals or exceeds the bolt’s strength (e.g., ASTM A563/A194 to suit A325/A490/A307, or metric property classes to match 8.8/10.9/12.9 fasteners).
- Choose the finish for the environment: Zinc for dry indoor, 304 for general outdoor, 316 for chlorides, HDG for exterior structural exposure.
- Check wrench size/clearance: Heavy hex has larger across-flat dimensions—verify socket/wrench access.
Installation Tips for Heavy Hex Nuts
- Start by hand to avoid cross-threading; confirm correct thread system (inch vs metric) and pitch.
- Use the specified procedure for structural joints (snug-tight → turn-of-nut / calibrated wrench / tensioning as required).
- Apply anti-seize on stainless pairs to reduce galling; avoid high-speed rundown.
- For HDG fasteners, use HDG nuts sized for coating thickness; follow structural torque/tension values.
- Use flat washers to spread load on softer materials or slotted holes; employ lock methods where vibration is present.
Heavy Hex Nut Size Notes
Heavy hex nuts use larger “across flats” dimensions than standard hex. Verify tool size from dimensional tables for your diameter (e.g., 3/4-10 heavy hex typically takes a 1-1/4" wrench). Always consult the governing standard (ASME/ASTM/ISO) for exact dimensions and compatible bolt grades.
Heavy Hex Nut Specifications
| Nut Sizes | Flats | Height |
| 1/4"-20 | 1/2" | 15/64" |
| 5/16"-18 | 9/16" | 19/64" |
| 3/8"-16 | 11/16" | 23/64" |
| 7/16"-14 | 3/4" | 27/64" |
| 5/8"-11 | 1-1/16" | 39/64" |
| 3/4"-10 | 1-1/4" | 47/64" |
| 7/8"-9 | 1-7/16" | 55/64" |
| 1"-8 | 1-5/8" | 63/64" |
| 1-1/8"-7 |
1-13/16"
|
1-7/64"
|
| 1-1/4"-7 | 2" | 1-7/32" |
| 1-1/2"-6 | 2-3/8" | 1-15/32" |
| 1-5/8"-5.5 | 2-9/16" | 1-19/32" |
| 1-3/4"-5 | 2-3/4" | 1-23/32" |
| 2"-4.5 | 3-1/8" | 1-31/32" |
Heavy Hex Nuts FAQs
A heavy hex nut is a thicker, wider version of a standard hex nut that offers more thread engagement and a larger bearing surface for high-load connections.
Use heavy hex when you need higher clamp load, stronger joints, larger washers/holes, or when pairing with heavy hex/structural bolts and anchor rods.
Yes. The “across flats” dimension is larger than standard hex for the same diameter, so verify socket/wrench size and clearance.
Match diameter and thread pitch exactly (e.g., 3/4-10, 1-8, M20-2.5) and select a nut grade/standard compatible with the bolt’s grade (ASTM A563/A194 to suit A325/A490/A307, or metric property classes to match 8.8/10.9/12.9).
Zinc plated for dry indoor; 304 stainless for general outdoor; 316 stainless for marine/chlorides; hot-dip galvanized for exterior structural exposure.
Yes, heavy hex is commonly used on anchor rods and embedded bolts for base plates and structural supports. Match grade and finish to the rod and environment.
Flat washers are recommended on slotted/oversized holes or soft materials to spread load; structural specifications often require hardened washers.
Follow torque/tension values from the governing standard, bolt grade, and lubrication condition. Structural connections may require calibrated torque or turn-of-nut procedures.
Apply a suitable anti-seize, tighten at moderate speed, and avoid over-torque; use compatible stainless grades.
No. Never mix inch and metric threads—diameter and pitch must match exactly.