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Author: Site Editor Publish Time: 2025-11-03 Origin: Site
The stainless steel carriage bolt, also known as a round head square neck bolt, is a popular fastener widely used in construction, woodworking, and solar mounting systems.
Designed with a smooth dome-shaped head and a square neck, it offers excellent resistance to loosening and provides a clean, finished look for both functional and aesthetic applications.
A carriage bolt is a type of bolt fastener featuring a round head and a square neck beneath it.
The square neck locks the bolt in place when inserted into a square hole or wood surface, preventing it from turning when tightening the nut.
Carriage bolts are commonly used with nuts and washers to form a secure joint in:
Solar mounting structures
Wood and metal connections
Furniture assembly
Automotive and mechanical equipment
| Item | Description |
|---|---|
| Product Name | Stainless Steel Carriage Bolt |
| Head Type | Round head, square neck |
| Thread Type | Full or partial thread |
| Material | Stainless Steel 304 / 316 / 316L |
| Diameter Range | M5 – M20 |
| Length Range | 20mm – 300mm |
| Surface Finish | Polished or passivated |
| Strength Grade | A2-70, A4-80 |
| Standard | DIN 603, ISO 8677, ASME B18.5 |
Made from 304 or 316 stainless steel, carriage bolts resist rust and oxidation — ideal for outdoor or marine environments.
The square neck fits into wood or metal slots, preventing the bolt from spinning during tightening. This ensures a stable and reliable connection.
The rounded head provides a neat, finished look, perfect for visible surfaces such as solar panel supports, furniture, and architectural projects.
The A2-70 and A4-80 stainless steel grades offer strong tensile performance, withstanding vibration and heavy loads without deformation.
A carriage bolt assembly consists of three main components:
| Component | Function |
|---|---|
| Bolt (Round Head + Square Neck) | Provides the main structural connection |
| Nut (Hex or Flange) | Tightens and secures the bolt in place |
| Washer (Flat or Spring) | Distributes load and prevents loosening |
When tightening the nut, the square neck of the bolt locks into the base material, eliminating the need for a wrench on the bolt head side — making installation faster and easier.
| Application Area | Usage |
|---|---|
| Solar Mounting Systems | Fixing support beams, rails, and brackets |
| Wood Structures | Joining beams, fences, decks, and furniture |
| Metal Frames | Connecting panels and frames |
| Automotive & Machinery | Securing covers, guards, and mechanical parts |
| Public Infrastructure | Used in bridges, walkways, and outdoor installations |
These stainless steel bolts are essential solar fasteners in modern solar PV mounting systems, providing both strength and corrosion resistance.
| Feature | Benefit |
|---|---|
| Material Durability | Stainless steel construction for long-term outdoor use |
| Anti-Loosening Function | Square neck locks into place |
| Aesthetic Design | Smooth dome head for visible applications |
| Easy Installation | No need to hold bolt head during tightening |
| Wide Compatibility | Works with nuts, washers, and mounting brackets |
| Grade | Composition | Key Properties | Application |
|---|---|---|---|
| A2-70 (SS304) | 18% Cr, 8% Ni | General corrosion resistance | Indoor and outdoor use |
| A4-80 (SS316) | 16% Cr, 10% Ni, 2% Mo | Marine and chemical resistance | Solar, marine, and industrial use |
| 316L | Low carbon variant | Better welding performance | Chemical processing or food-grade systems |
Choosing the right stainless steel bolt grade ensures reliability under different environmental conditions.
In solar panel mounting structures, carriage bolts are used to connect rails, posts, and ground screws.
Their square neck design prevents rotation during installation, while the stainless steel material resists corrosion in outdoor environments.
Typical solar assembly includes:
Stainless steel carriage bolt
Spring washer
Flat washer
Hex nut
These components form a secure and vibration-resistant connection for long-term performance.
Drill or align a square hole or use a pre-designed slot in the metal or wood base.
Insert the carriage bolt into the hole; the square neck fits tightly to prevent rotation.
Place a washer and nut on the threaded end.
Tighten the nut using a wrench or socket until secure.
Check for alignment and ensure the bolt is firmly seated.
Regularly check for loosening in high-vibration environments.
Apply anti-seize compound for marine or coastal installations.
Use matching stainless steel nuts and washers to avoid galvanic corrosion.
Clean exposed bolt heads periodically for aesthetic maintenance.
The stainless steel carriage bolt is a robust and reliable fastener that combines strength, safety, and visual appeal.
Whether used in solar mounting systems, woodworking, or industrial structures, it ensures long-term performance and resistance to environmental challenges.
With 316-grade stainless steel bolts, you can achieve maximum durability, making them the ideal choice for outdoor and renewable energy projects.
1. What is a carriage bolt used for?
It is used to fasten metal or wood components where a smooth, rounded finish is desired — such as in solar systems, furniture, or decking.
2. What is the difference between a carriage bolt and a hex bolt?
A carriage bolt has a round head and square neck to prevent rotation, while a hex bolt has a hexagonal head for wrench tightening.
3. Are stainless steel carriage bolts rust-proof?
Yes, especially A4-80 (316 stainless steel) carriage bolts, which provide excellent corrosion resistance in outdoor and marine conditions.
4. What size carriage bolts are most common?
Common sizes range from M6 to M12, depending on the application and structural load.
5. Can I use carriage bolts for solar installations?
Absolutely. Stainless steel carriage bolts are widely used in solar mounting systems to secure rails, brackets, and other fastened parts.
