must have been lucky Owen.
Its an International Drivers Permit (IDP), not a licence. Basically a UN sanctioned translation of home country licence. Has to have home country licence with it.
From Australia driving overseas wife and I both had MR (Medium Rigid, two axles greater than 8 Mt) in Aus specifically for trip. As mentioned already, the boundary from car to truck is 4.5Mt in Aus, 3.5Mt Asia, Europe and IDP. LR (Light Rigid) was same price.
Saved a lot of bother several times having all the circles in the IDP stamped. Notably when stopped in Germany and Cambodia but also Russia.
Coming into Aus is obscure. Not helped that each of seven states deals with drivers licencing a bit differently.
Here's South Australia which is most explicit. An IDP is required.
https://www.sa.gov.au/topics/transp...al-motorists/driving-with-an-overseas-licence
NSW is usually the most stroppy. In my experience Aus Traffic Police tend to be revenue driven rather than driver behaviour.
Here's one example of a company that provide MR licence.
http://www.transtrain.com.au/truck-a-bus-licences/medium-rigid-mr.html
I have to contact Automobile Association Australia soon (each state has its own automobile organisation, AAA provides services through state orgs). Contact had useful info and advice before I traveled and understood the oddity of the different weights in different countries. Its been that way forever but is apparently on the agenda when countries meet for review in a few years. I'll ask.