This is what the NSW Guidelines actually state:
"The A-frame and its components must be certified to comply with the intent of Australian Design Rule (ADR) 62 Mechanical connections between vehicles. All couplings must be marked with the manufacturer’s name or trademark and the rated capacity."
One might ague what the word 'couplings' means, however, 'couplings' is a plural noun meaning 'a device for connecting parts of machinery'. Therefore, whilst there are many parts involved (hitch, bars, receivers, chains, cables, bolts, etc.,) 'couplings' is the whole, not individual parts.
The proof of the pudding is that all such couplings sold and fitted in every State have one plate or stamping that marks the manufacturer and the rated capacity somewhere on the body of the device and not on every component.
Good luck telling the expert that he is wrong, but if he examines A-Frames supplied and fitted by commercial suppliers he will be convinced.
