Trailer U-Bolts — Round & Square Suspension U-Bolts

TractorTrailerParts manufactures heavy-duty trailer U-bolts — round and square bend — in 3/8", 1/2", 9/16" and 5/8" diameters with matching axle tie-plates, grade-8 nuts and hardened washers. Supplied in bulk to US wholesale trailer parts distributors, suspension shops and OEM trailer manufacturers.

Round and square trailer suspension U-bolts with matching axle tie-plates and grade-8 nuts

Trailer U-Bolt Range

  • Round trailer U-bolts (for round axles)
  • Square trailer U-bolts (for square axles)
  • Diameters: 3/8", 1/2", 9/16", 5/8"
  • Inside widths: 2", 2-3/8", 3" (custom on request)
  • U-bolts with grade-8 nuts and washers
  • Matching axle tie-plates & spring seats
  • UNC and UNF thread options
  • Custom U-bolts to drawing, length or bend

Key Features & Specifications

  • Rod diameters: 3/8" / 1/2" / 9/16" / 5/8" / custom
  • Bend styles: round (semi-circular) and square (90° corners)
  • Grades: medium-carbon steel, grade-5 / grade-8
  • Thread: UNC and UNF, rolled threads for strength
  • Finishes: zinc-plated, hot-dip galvanized, raw / black oxide
  • Supplied as bolt only, kit (with nuts & washers), or full set with tie-plate
  • Bulk packaging — bags, boxes or palletized for container shipment

Applications

  • Trailer leaf-spring suspension
  • Trailer axle mounting
  • Agricultural & farm trailers
  • Utility & cargo trailers
  • Boat trailers
  • Trailer suspension repair / replacement
  • OEM trailer assemblies

Technical Sourcing

Send required diameter, inside width, leg length, thread spec and finish — we'll quote bulk pricing per piece or per kit for US distributors and trailer OEMs.

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Trailer U-Bolt FAQs

What are trailer U-bolts used for?

Trailer U-bolts clamp the axle to the leaf-spring suspension using a tie-plate on top and nuts on the bottom of the U. They're one of the highest-stress fasteners on a trailer, securing the entire axle assembly to the springs and frame.

How are trailer U-bolts measured?

Three dimensions: rod diameter (3/8", 1/2", 9/16"), inside width between legs (must match the axle — typically 2", 2-3/8" or 3"), and total leg length (long enough to clear the spring stack, tie-plate and nut).

What torque should trailer U-bolts be tightened to?

General torque guide: 3/8" to 30–50 ft-lbs, 1/2" to 70–90 ft-lbs, 9/16" to 100–130 ft-lbs, 5/8" to 160–200 ft-lbs. Tighten in a cross pattern, re-torque after the first 50 miles, and follow the axle manufacturer's spec when available.

What's the difference between round and square U-bolts?

Round U-bolts have a curved (semi-circular) top and fit round trailer axles. Square U-bolts have a flat top with two 90° bends and fit square trailer axles. Diameter and grade must match the axle's spring-seat width and load rating.