SPARKWHIZ Trailer U-Bolt Kit for 3" Round Axles — 7 1/8" Long, 1/2" Dia, Fits 5,200–7,000 lb Trailers

SPARKWHIZ Trailer U Bolt Kit is a complete mounting set designed to secure 3" round axles on 5,200–7,000 lb trailer assemblies using 7 1/8" long, 1/2" diameter U-bolts and matching plates and hardware.

When you need to fasten a heavy-duty trailer axle to leaf springs, the right hardware matters for safety and stability. This SPARKWHIZ kit supplies everything required to clamp a 3" round axle to standard 1.75" or 2" trailer springs: four U-bolts, tie plates sized for 1-3/4" springs, and the correct nuts to finish the installation. Built from durable steel with corrosion resistance, the components are sized and specified for axles in the 5,200–7,000 lb range to suit mid-capacity trailers, haulers, and equipment carriers.

What components are included and how do they fit together?

The kit includes four 7 1/8" long U-bolts with a 1/2" diameter, eight 1/2"-20 hex nuts, and two tie plates sized to pair with 1-3/4" leaf springs. Each U-bolt wraps under the axle and through the tie plate so that the nuts draw the assembly tight against the spring pack.

• Four U-bolts: 7 1/8" length, 1/2" diameter
• Eight hex nuts: 1/2"-20 thread pitch
• Two tie plates designed for 1-3/4" leaf springs
• Fits 1.75" or 2" spring widths when installed correctly

Which axles and trailers is this U-bolt kit compatible with?

This kit is intended for round axle beams measuring 3" in diameter and for axle systems rated between 5,200 and 7,000 pounds. It’s commonly used on single- and tandem-axle utility trailers, boat trailers, and light equipment trailers that use standard leaf springs.

• Axle beam diameter: 3" round
• Weight capacity range: 5,200–7,000 lbs
• Spring compatibility: 1.75" or 2" trailer springs
• Typical trailer types: utility, boat, equipment, livestock

How should I torque and maintain these U-bolts for safe performance?

Tightening to the correct torque prevents loosening and ensures clamping force without overstressing the hardware. The recommended torque range for this kit is 65 to 75 ft-lbs; check torque after initial use and periodically during regular trailer maintenance.

• Torque specification: minimum 65 ft-lbs, maximum 75 ft-lbs
• Recheck torque after first 50–100 miles and at regular service intervals
• Inspect for corrosion, thread wear, and plate deformation
• Replace any bent or heavily corroded parts immediately

Why choose SPARKWHIZ steel U-bolts over generic fasteners?

SPARKWHIZ parts are manufactured to match common trailer standards and use thicker steel and protective finishes to resist rust and prolong life under road and weather exposure. Properly sized hardware also helps preserve brake alignment and suspension performance.

• Durable steel construction with corrosion-resistant finish
• Correct sizing reduces risk of spring or axle movement
• Complete set eliminates mismatched hardware issues
• Supports consistent braking and suspension geometry

Who is this for? The SPARKWHIZ Trailer U Bolt Kit is aimed at trailer owners, fleet managers, and DIY mechanics who need a ready-to-install, correctly sized U-bolt solution for 3" axles rated 5,200–7,000 lbs. If you service utility or equipment trailers and want a reliable set of U-bolts, tie plates, and nuts that match common leaf spring widths and torque specifications, this kit is built for you.