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Rated Shackles and Bow Shackles caravans, campers, and trailers
Rated shackles are a requirement for all caravans and trailers under 3.5t. Trailers over 3.5t require Grade 80 chain and chain holders.
When selecting dee or bow shackles buyer need to be aware of the two calculations available for their purchase.
The towing ATM rating is determined by calculation.
The Breaking capacity of the shackle is a different calculation,
Standard dee shackles cannot be proved to be compatible therefore rated shackles fulfil the requirement of chain compatibility.
The marking on a Rated Shackle is the Safe Working Load Limit (WLL)
The Breaking load limit (BLL) for rated shackle is WLL x 6, Example, a 1 tonne rated Dee Shackle has a BLL of 1t x 6 = 6t (Breaking Load Limit)
Calculate the ATM as follows, BLL / 1.5 = 6t / 1.5 = 4t
Therefore, a 1t Dee Shackle can be used on trailers up to 4t. Please see the following table for more ratings
0.75t Dee Shackle = 3t ATM Caravan
1t Dee Shackle = 4t ATM Caravan
1.5t Dee Shackle = 6t ATM Caravan
2t Dee Shackle = 8t ATM Caravan
Note: The design of the attachment to the drawbar must have sufficient load capacity to match the rating of the required chain.
However, a dee shackle must be compatible with the safety chain, and the safety chain must be identified with at least the same capacity as the ATM.
Rated shackles are tested and rated according to AS2321 Short Link Chain for Lifting Purposes.
Bow Shackles Breaking Capacity Calculations
When bow shackles are attached to a towbar the BLL (brake load limit} is 6 x the stamped WLL (weight load limit). They are as follows:
0.75t Dee Shackle = 4.5t
1t Dee Shackle = 6t
1.5t Dee Shackle = 9t
2t Dee Shackle = 12t
Trailers over 2.5t must have two safety chains. Further, each chain must be of the same capacity or exceed the loading of the ATM.
Australian Standards require safety chains on trailers over 3.5t to be connected to the trailer via safety chain holders or approved high tensile links. Dee shackles are not an authorised device and therefore not permitted.
Trailers Under 2.5t
If the trailer does not exceed 2.5 tonnes ATM, it must have at least one safety chain complying with Australian Standard AS 4177.4-1994, or Australian Standard AS 4177.4-2004 ‘Caravan and light trailer towing components – Part 4.
Trailers 2.5 To 3.5t
Two safety chains of a designation of 3500 kg or higher for each chain.
Trailers Over 3.5t
According to Standard AS 4177.4-1994 and Australian Standard AS 4177.4–2004, trailers over 3.5 tonnes ATM must have two safety chains made from steel of a minimum 800 MPa breaking stress.
Chains also conform to the mechanical properties of Grade-T chain as specified in Australian Standard AS 2321-1979 ‘Short Link Chain for Lifting.
Purposes (non-calibrated), or Australian Standard AS 2321–2006 Short Link Chain for Lifting Purposes.
Ultimately, you’ll need to go in for a chain sized such that the minimum breaking load exceeds the ATM.
Further, Couplemate sells only the best quality dee shackles and safety chains.