Square Nuts
What Are Square Nuts?
Square nuts are four-sided finish nuts that provide a larger bearing surface than standard hex nuts. The increased face area improves bite against flat stock and channels, making them harder to loosen and less likely to round over during repeated tighten/loosen cycles. Their shape also allows tool-free tightening with pliers in blind or tight locations.
Benefits of Square Nuts
- Large contact area: Greater clamp force on sheet, channel, or plate assemblies.
- Easy handling in tight spaces: Two flat sides align naturally for plier or adjustable-wrench grip.
- Resists cam-out and rounding: Four wide faces reduce edge damage compared to hex.
- Works with flat washers: Spreads load and prevents marring of softer materials.
Square Nut Materials & Finishes
- 304 Stainless Steel: General-purpose corrosion resistance for freshwater or non-salt environments.
- 316 Stainless Steel: Enhanced corrosion resistance for saltwater, marine, and harsh outdoor use.
- Zinc-Plated Steel: Economical indoor/sheltered corrosion protection with a bright finish.
- Hot-Dip Galvanized Steel: Thick zinc coating for rugged outdoor exposure and structural work.
Common Applications for Square Nuts
- Channel, strut, and plate assemblies
- Timber connectors and restoration hardware
- Electrical & mechanical equipment mounting
- Railings, fences, signage, and architectural metalwork
Installation Tips for Square Nuts
- Pair with a flat washer to maximize bearing area and protect finishes.
- Start threads by hand to prevent cross-threading, then tighten with pliers, an adjustable wrench, or a socket sized to the across-flats dimension.
- For galvanized systems, match hot-dip galvanized bolts and washers for proper fit and corrosion compatibility.
- Follow torque guidance for the bolt grade and size; avoid over-torque that could dish thin plate.
How to Choose the Right Square Nut
- Thread size & pitch: Match the fastener (e.g., 1/4-20, 3/8-16, M10-1.5).
- Environment: Choose 316 for marine/salt; 304 for general outdoor; zinc for indoor; hot-dip galvanized for heavy outdoor exposure.
- Load & fit: Verify across-flats and thickness against your channel or plate clearances.
Square Nut Specifications - 304 Stainless Steel
| Size |
Across Flats (Max-Min) |
Thickness (Max-Min) |
Square Shape |
| #4 | 0.250-0.241 | 0.098-0.087 | Flat |
| #6 | 0.312-0.302 | 0.114-0.102 | Flat & Beveled |
| #8 | 0.344-0.310 | 0.130-0.117 | Beveled |
| #10 | 0.375-0.362 | 0.130-0.117 | Beveled |
| 1/4" | 0.438-0.423 | 0.193-0.178 | Flat & Beveled |
| 5/16" | 0.562-0.545 | 0.225-0.208 | Beveled |
| 3/8" | 0.625-0.607 | 0.257-0.239 | Beveled |
| 1/2" | 0.812-0.788 | 0.458-0.418 | Beveled |
| 5/8" | 1.000-0.969 | 0.569-0.525 | Beveled |
| 3/4" | 1.125-1.088 | 0.680-0.632 | Beveled |
Square Nut Specifications - 316 Stainless Steel
| Size |
Across Flats (Max-Min) |
Thickness (Max-Min) |
Square Shape |
| 1/4" | 0.438-0.423 | 0.193-0.178 | Flat & Beveled |
| 5/16" | 0.562-0.545 | 0.225-0.208 | Beveled |
| 3/8" | 0.625-0.607 | 0.257-0.239 | Beveled |
| 1/2" | 0.812-0.788 | 0.458-0.418 | Beveled |
| 5/8" | 1.000-0.969 | 0.569-0.525 | Beveled |
| 3/4" | 1.125-1.088 | 0.680-0.632 | Beveled |
Square Nut Specifications - Zinc Plated Steel
| Nut Size | Width Across Flats | Thickness |
| 1/4" | Max 0.438-Min 0.423 | Max 0.235-Min 0.203 |
| 5/16" | Max 0.562-Min 0.545 | Max 0.283-Min 0.249 |
| 3/8" | Max 0.625-Min 0.607 | Max 0.346-Min 0.310 |
| 7/16" | Max 0.750-Min 0.728 | Max 0.394-Min 0.356 |
| 1/2" | Max 0.812-Min 0.788 | Max 0.458-Min 0.418 |
| 5/8" | Max 1.000-Min 0.969 | Max 0.569-Min 0.525 |
| 3/4" | Max 1.125-Min 1.088 | Max 0.680-Min 0.632 |
| 7/8" | Max 1.312-Min 1.269 | Max 0.792-Min 0.740 |
| 1" | Max 1.500-Min 1.450 | Max 0.903-Min 0.847 |
Square Nut Specifications - Hot Dip Galvanized Steel
| Nut Size | Width Across Flats | Thickness |
| 1/4"-20 | Max 0.438-Min 0.423 | Max 0.235-Min 0.203 |
| 5/16"-18 | Max 0.562-Min 0.545 | Max 0.283-Min 0.249 |
| 3/8"-16 | Max 0.625-Min 0.607 | Max 0.346- Min 0.310 |
| 7/16"-14 | Max 0.750-Min 0.728 | Max 0.394- Min 0.356 |
| 1/2"-13 | Max 0.812-Min 0.788 | Max 0.458-Min 0.418 |
| 5/8"-11 | Max 1.000-Min 0.969 | Max 0.569-Min 0.525 |
| 3/4"-10 | Max 1.125-Min 1.088 | Max 0.680-Min 0.632 |
| 7/8"-9 | Max 1.312-Min 1.269 | Max 0.792-Min 0.740 |
| 1"-8 | Max 1.500-Min 1.450 | Max 0.903-Min 0.847 |
| 1-1/8"-7 | Max 1.688-Min 1.631 | Max 1.030-Min 0.970 |
| 1-1/2"-6 | Max 2.250- Min 2.175 | Max 1.348-Min 1.276 |
Square Nuts — Frequently Asked Questions (FAQ)
They’re four-sided nuts used on channels, plates, and timber or restoration hardware where a wide bearing surface and easy tool grip are helpful.
Strength depends on material and grade. Square nuts aren’t inherently stronger, but their larger face area provides better bearing on flat stock.
Use 304 for general outdoor/freshwater exposure; use 316 in marine, salt, or highly corrosive environments.
Zinc plating is a thin electroplated coating for light/indoor corrosion protection; hot-dip galvanizing is a thick, rugged zinc layer for long-term outdoor use.
Start by hand, then use pliers, an adjustable wrench, or a correctly sized socket on the flats. Add a flat washer to spread load on sheet or wood.
Yes. The four wide faces make them easier to hold with pliers when you can’t get a hex socket or box wrench on the nut.
It’s best to match materials and finishes to avoid galvanic corrosion and fit issues—use galvanized with galvanized, stainless with stainless.
Match the nut’s thread size and pitch to your bolt or stud (e.g., 3/8-16). Also confirm across-flats and thickness clearances in the channel or plate.