The Department of Transport Driver and Vehicle Services in WA ( https://www.transport.wa.gov.au/) pulished the following Vehicle and Standards Circular to Industry – Safety Chains and Shackles for Trailers under 4.5 tonnes ATM built after 1991.
The original document can be found https://www.transport.wa.gov.au/mediaFiles/licensing/lbu_vs_ci_119.pdf/group