39mm Round Spring U-Bolt Kits – Galvanised

Part No: UK39R Category: Tag:

$39.00 - $46.00

Couplemate™️ 39mm Round Spring U-Bolt Kits provide a strong and secure connection for trailer, caravan, and camper leaf springs.

Suits 39mm or 40mm round axles.
Uses galvanised u-bolts and plates (great for boat trailers).
Easily DIY spring and axle maintenance at home with this complete kit.

See technical diagram for u-bolt measurements.

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39mm Round Spring U-Bolt Kits | Hot-Dip Galvanised

The Couplemate™ 39mm u-bolt kit for round axles includes Galvanised u-bolts, nylock nuts, and fish plates.

Spring U-Bolt Kits are designed to secure leaf springs to trailer and caravan axles safely. U-bolts link your trailer and the road; hence, it is important to use u-bolts made from high-quality materials. 

Need new springs? See our range of leaf springs.

This U-Bolt Kit is supplied with:

  • 4 x U-Bolts (choose preferred length)
  • 8 x Washers
  • 8 x Nyloc nuts
  • 2 x Fish Plates
  • 2 x Axle Pads/Spacers

39mm Round U-Bolt Specifications

U-Bolts are measured on their internal dimensions to ensure proper fit and alignment with the equipment. See our technical diagram for a visual reference.

  • Coating: Traditional hot-dipped galvanised
  • Thread: 1/2″ UNF (12.7mm)
  • Internal U-Bolt Width: 39mm
  • Internal U-Bolt Leg Lengths:
    • 100mm (4″)
    • 115mm (4.5″)
    • 125mm (5″)
    • 140mm (5.5″)
    • 150mm (6″)

Couplemate™️ supplies these 39mm round u-bolt kits for leaf spring suspension systems (usually for axles with Holden or Composite bearings). Shop replacement 39mm Round Trailer Axles.

Installation (User Guide)

Couplemate™️ 39mm U-Bolt Kits are easy for trailer spring maintenance.

  • Place U-shaped curve over axle beam.
  • Align the centre spring bolt and U-bolt legs with the fish plate holes.
  • Secure fish plate to leaf spring through supplied washers and nylock nuts. Tighten nuts to 60Nm with a socket.

Important: Check U-bolts and re-tighten nuts after the first trip and every 250 km thereafter.

Safety Precautions

Road safety is essential for all Australians. Please ensure to check and re-tighten after the first trip and every 250 km thereafter.

  • Do not re-use nyloc nuts. Nyloc nuts are often less effective after the first use. This is because the nylon material (the key component of a nyloc nut) has already once conformed to the thread profile. 
  • Do not use a rattle gun to tighten. Rattle guns often tighten U-bolts too fast, too tight, and unevenly. This can cause the nylon to overheat and risk undue wear. 
  • Ensure the axle has welded axle pads. If not, use the axle pads supplied with the spring U-bolt kit.

See the range of other trailers and towing safety parts.

Available U Bolt Kits


Additional information

Weight3.9 kg
Dimensions20 × 15 × 5 cm


Internal Length

100mm, 115mm, 125mm, 140mm, 150mm

Internal Width



1/2" UNF

Torque Setting


Our Service Lifetime Warranty

Our goods come with guarantees that cannot be excluded under the Australian Consumer Law. You are entitled to a replacement or refund for a major failure and compensation for any other reasonably foreseeable loss or damage. You are also entitled to have the goods repaired or replaced if the goods fail to be of acceptable quality and the failure does not amount to a major failure.

Couplemate™ is a manufacturer and vendor of high-quality towing, trailer, and caravan components. Couplemate™ Core Goods and Custom Work are guaranteed to be free of defects for the service lifetime of the product when used as intended.

Warranties are non-transferrable and Couplemate™ requires satisfactory proof of purchase prior to issuing a remedy. The full Couplemate™ Warranty Policy can be found in the Terms & Conditions: Section 8 – Consumer Guarantees & Warranty.

Warranties are in addition to your rights under the Australian Consumer Law. If something is wrong with your order, please contact our team.

60-Day Returns

After 60 years of experience, we know that life has its unpredictable moments.

All Couplemate™ orders (online, over the phone, or in-store) have a 60 day period for change-of-mind returns and exchanges. There are some items that can’t be returned and some returns may incur a 15% restocking fee.

You can view our full policy for change-of-mind returns here.


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