Answer

ATM stands for Aggregate Trailer Mass, and as the name suggests this term is only applicable in the case of trailers. 

Queensland Government categorises trailers according to their ATM. A trailer of ATM between 0 and 3500 (including 3500) kilograms is classified as a light unit and any trailer above is considered heavy. Information on the ATM of your particular trailer can be found on past registration labels, or renewal documents. Heavy and light units require different safety inspection some of which may be scheduled each year.

ACE Mobile Safety Certificates can conduct the required Safety inspection for trailers up to and including 10,000 kgs (10 T) ATM.