VSB1 states - Trailers must be fitted with safety chains that are marked in accordance with the relevant Australian Standard complying with the following:

• Trailers that do not exceed 2.5 tonnes ATM 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: Safety chains up to 3500kg capacity
• Trailers over 2.5 tonnes and not exceeding 3.5 tonnes ATM must have two safety chains of designation of 3500kg complying with Australian Standard AS 4177.4-1994 or Australian Standard AS 4177.4-2004

Trailer Safety chains are provided in four designations as per the Australian Standard and are referenced according to the aggregate trailer mass. The designations and the corresponding aggregate trailer masses are in in the rating table below.