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When a loose axle clamp or a corroded fastener puts your trailer out of service before launch day, you need a U-bolt you can trust. These square U-bolts are designed for boat trailer builders, marine fabricators, and DIY enthusiasts who demand a secure, rust-resistant hold in wet and salt-spray environments.
Each U-bolt is formed from 304 stainless steel with a black oxide finish, giving it both corrosion resistance and a clean, low-profile appearance. Thread diameters span M6, M8, and M10; bolt lengths range from approximately 20 mm (0.79 in) to 150 mm (5.91 in); and inside widths run from approximately 50 mm (1.97 in) to 200 mm (7.87 in). Every set ships with matching hex nuts pre-threaded for quick assembly.
Typical applications include boat trailer axle clamps, leaf-spring U-bolt replacement, pipe and conduit mounting on marine structures, and square-tube frame fabrication for utility trailers. Whether you are searching for M8 square U-bolts for trailer axle repair or M10 stainless U-bolts for heavy-duty pipe clamps, these fasteners cover the most common metric sizes in one listing.
| Material | 304 Stainless Steel |
|---|---|
| Finish | Black Oxide |
| Bolt Shape | Square (90° bend) |
| Thread Diameter | M6 / M8 / M10 |
| Thread Pitch | M6 × 1.0 mm | M8 × 1.25 mm | M10 × 1.5 mm (ISO Coarse) |
| Bolt Length (L) | See variant options |
| Inside Width (W) | See variant options |
| Included Hardware | Hex nuts (quantity per set: 1 Pcs or 2 Pcs — see variant options) |
| Tensile Strength | See variant options |
| Typical Application | Boat trailer axle clamps, pipe mounting, square-tube frame fabrication |
| Weight | See variant options |
Measure the outer diameter (or outer width for square axles) of your axle housing. The inside width (W) of the U-bolt should match or be very slightly larger than that measurement. Then select a bolt length (L) long enough to pass through your spring plate and leave at least two full thread pitches exposed for the nut. Use the Size option above to find the combination that fits your axle.
304 stainless steel provides solid tensile strength suitable for typical light-to-medium boat trailer axle loads. For heavy-duty commercial trailers or applications exceeding standard load ratings, consult your trailer manufacturer's torque and load specifications and verify the bolt grade meets your requirements before installation.
Yes. The base material is 304 stainless steel, which is inherently corrosion-resistant. The black oxide finish adds a secondary barrier against surface oxidation. For prolonged submersion or highly aggressive salt environments, applying a thin coat of marine-grade anti-seize compound on the threads before assembly is recommended to prevent galling.
In the size format shown (e.g., M8×50mm×90mm), the first number is the thread diameter, the second is the bolt leg length (L) — the distance from the bend to the end of the threaded rod — and the third is the inside width (W) — the gap between the two parallel legs. Match the inside width to your axle or pipe outer dimension and the leg length to your spring plate stack height.
Yes, matching hex nuts are included with every U-bolt. The nuts are manufactured from 304 stainless steel to match the bolt material and prevent galvanic corrosion. The quantity (1 Pcs or 2 Pcs) refers to the number of complete U-bolt-plus-nut sets in the package — select your preferred quantity in the Amount option above.
Absolutely. The square bend geometry makes these U-bolts well-suited for clamping round pipes, conduit, and tubing to flat mounting surfaces such as structural steel, wooden beams, or aluminum extrusions. They are commonly used in marine pipe runs, dock hardware, and utility trailer frame builds wherever a secure, corrosion-resistant clamp is needed.
Standard metric wrenches or sockets are all that is required. Use the correct size for the hex nut (M6 nuts typically take a 10 mm wrench, M8 a 13 mm, and M10 a 17 mm). Torque to the specification recommended by your trailer or equipment manufacturer. Applying thread-locking compound or a nylon-insert lock nut is advisable in high-vibration applications.
