Choosing The Right D-Shackle For Your Towing Setup

A D-shackle (also called a bow shackle or chain shackle) is typically a U-shaped metal connector with a pin through the open end, used to attach safety chains from your trailer to the towing vehicle. It is a critical safety device, used to reduce the risk of an accident should the trailer decouple from the towing vehicle. When selecting the correct D-shackle for towing in New Zealand, there are specific considerations to ensure safety, compliance, and reliability.

According to the New Zealand Code of Practice NZS 5467:1993, safety connections, including chains and shackles, must have a minimum breaking strength equal to at least twice the maximum towed mass (MTM). For example, if towing a trailer with a combined tare weight and load of 2,000 kg, the safety connection must have a combined minimum breaking strength of 4,000 kg.

Note: The Working Load Limit (WLL) of a D-shackle is not equivalent to its break strength. Always refer to the manufacturer’s break strength when selecting D-shackles for your towing application.

Important Considerations When Selecting D-Shackles

• Chains and shackles must have a break strength at least 2× the maximum trailer mass (MTM).
• Up to 2,000 kg: must have one safety chain, unless fitted with a breakaway brake.
• 2,000–2,500 kg: must have two safety chains unless fitted with a breakaway brake.
• 2,500–3,500 kg: require a breakaway brake system and two safety chains.
• Chains must be long enough to allow turning but short enough to prevent dragging.
• Inspect D-shackles before each trip for cracks, rust, or deformation.
• Keep pins tightly screwed or cottered; loose pins can fail under vibration.
• Avoid welding or modifying shackles; they must be used as rated.
• Pin Type: Choose shackles with bolt-type pins secured with nuts and cotter pins to prevent loosening under vibration.
• Bow Shape: A large rounded bow accommodates thick safety chains and allows multi-directional movement, reducing wear and enhancing safety.

Tip: Always choose a D-shackle with a breaking strength at least 2× the MTM of the trailer. For example, for a trailer with an MTM of 2,000 kg, a single 10 mm Grade S D-shackle (WLL 1T) is sufficient, as the breaking strength = 58.9 kN, or approximately 6,000 kg.