I regularly tow 2.5-3 tonne and as such prefer a fixed tow ball, in this case with a 50mm ball and coupling. In addition I have a 2.5 tonne trailer with 1 7/8" coupling.
I have a CM convert-a-ball which once greased up is pretty mucky to change - as I guess they all are. https://www.trailerpartsnz.com/product_info.php/towball-convert-ball-set-p-1800
Trojan have two types, their older Duo Ball and the new Multi Ball
Does anyone have any experience of the Trojan balls especially the newer Multi Ball?