What Is a Square Nut?
Square nuts are a type of standard fastener. They feature a square shape with internal threads and are used in conjunction with bolts. Square nuts can be used in slots, effectively preventing rotation when screws are tightened. Primary materials include leaded brass (H59, 3604, 3602), stainless steel (201, 301, 304, 316, etc.), aluminum alloy, and alloy steel. Square nuts are widely used in construction, building materials, home improvement, industrial and mining, transportation, and power industries.
Common sizes for square nuts range from M3 to M16, with standards including DIN 557, DIN 928.
Characteristics
- A square nut is a type of welded nut that is fused between two components by melting metal at high temperatures to achieve a secure fastening. This connection provides superior holding strength and is less prone to loosening or detachment.
- Compared to other nuts, square nuts offer greater load-bearing capacity due to their square heads, thereby enhancing the safety of fasteners to a certain extent.
- Compact size, widely applicable in various scenarios.
- Provides a larger torque transfer area, reducing the risk of nut slippage or loosening, with anti-slip performance 35% higher than hex nuts (ASTM F1574 test data).
- Easy installation—simply rotate 90° (hex nuts require only 60°)
Material of Square Nut
- Stainless steel: Excellent wear resistance, corrosion resistance, and rust prevention.
- Carbon steel: High strength and easy to machine.
- Brass: Good electrical conductivity and corrosion resistance.
- Nylon/Plastic: Lightweight and corrosion resistant.
Types of Square Nuts
Standard Square Nut
The most common and fundamental type of square nut features a standard square shape, with thickness and side length conforming to international or national standards.
Thin Square Nut
The thickness is significantly less than that of standard square nuts, primarily used in space-constrained applications or as lock nuts.
Heavy Square Nut
Compared to standard square nuts, these feature greater thickness and larger side lengths, designed for high-strength, high-load applications.
Square Weld Nut
Features solder points or protrusions at the base for direct soldering onto metal plates or structural components.
Square Lock Nut
Square nuts that achieve anti-loosening functionality through structural deformation, nylon inserts, or mating washers.
Mechanical Properties
| Carbon Steel | ||||||||||
| MECHANICAL PROPERTY | PROPERTY CLASS | |||||||||
| 4.8 | 5.6 | 5.8 | 6.8 | 8.8 Up to M16 | 8.8 Over M16 | 9.8 | 10.9 | 12.9 | ||
| TensileStrength(Rm, N/mm²) | nom. | 400 | 500 | 600 | 800 | 900 | 1000 | 1200 | ||
| min. | 420 | 500 | 520 | 600 | 800 | 830 | 900 | 1040 | 1220 | |
| VickersHardness | min. | 130 | 155 | 160 | 190 | 250 | 255 | 290 | 320 | 385 |
| max | 250 | 320 | 336 | 360 | 380 | 435 | ||||
| BrinellHardness | min. | 124 | 147 | 152 | 181 | 319 | 242 | 266 | 295 | 353 |
| max | 238 | 385 | 319 | 342 | 363 | 412 | ||||
| RockwellHardness | min. HR | 71 | 79 | 82 | 89 | – | ||||
| HRC | – | 20 | 23 | 28 | 32 | 39 | ||||
| HR | – | 99 | – | |||||||
| max HR | – | 32 | 34 | 37 | 39 | 44 | ||||
| Yield Stress ReL.N/mm² | nom. | 320 | 300 | 400 | 480 | – | ||||
| min. | 340 | 300 | 420 | 480 | – | |||||
| Stress at permanentset limit N/mm² | nom. | – | 640 | 720 | 900 | 1080 | ||||
| min. | – | 640 | 660 | 720 | 940 | 1100 | ||||
| Stainless Steel | |||||||
| Steel group | Steel grade | Strength class | Tensile strength N/mm2 | Tensile strength PSI | Dia range | Nut Load N/mm2 | Characteristics |
| Austenitic | A1, A2 | 50 | 500 | 70,000 | <=M39 | 500 | Soft; cold worked, turned and soft pressed fasteners |
| A2, A4 | 70 | 700 | 100,000 | <=M20 | 700 | Cold worked, normal strength formed fasteners | |
| A2, A4 | 80 | 800 | 118,000 | <=M20 | 800 | Extreme cold worked, high strength, special applications | |
How to Select Square Nuts?
Strength Matching
- Nut grade ≥ Bolt grade (e.g.: Grade 8 bolt → Grade 8 nut)
Thread Type
- Metric (M)
- Imperial (UNC / UNF)
Surface Treatment
- Zinc plated：Dry indoor
- Hot-dip galvanized：Industrial outdoor
- 316 stainless steel：Chemical/salt spray
Installation Space
- Normal space: Standard height
- Confined space: Low-profile version (-30% height)
Applications of Square Nuts
- Machinery Manufacturing: Machine tools, industrial equipment, transportation machinery, etc.
- Construction Engineering: Steel structure connections, metal door and window installation, and bracket fastening—suitable for applications requiring high torque.
- Railway and Transportation Equipment: Fastening of track facilities, signaling equipment, and support systems.
- Furniture and Woodworking Assembly: Designed for square holes or mortise-and-tenon joints, suitable for office furniture and cabinet installation.
- Electrical Equipment: Brass or stainless steel square nuts are used in conductive, grounding, or instrumentation equipment.
