The trailer only exists as a combination. These guides cover tow ratings, GCM, 50 mm balls, pintle and gooseneck couplings, weight-distribution hitches and the sway that shows up at 95 km/h on the Hume.
ADR 62 treats a coupling as a rated, lockable mechanical connection. The 50 mm ball is the Australian light-trailer default. Pintle and gooseneck exist when rating, articulation or deck layout run out.
A weight-distribution hitch puts load back on the steer axle. Sway control damps yaw. Neither raises ATM or GCM, and neither fixes a trailer loaded over the tail or towed with a soft rear tyre.
The legal combination is the lowest of ATM, GTM, GCM, the vehicle’s tow rating, the towbar and the coupling. Towball download of about 8–10 per cent is how that combination stays on the road.