For example: https://mcalpineplumbing.com/traps/shower-traps-accessories/st90cp10c-90mm-shower-trap - I assume that "water seal" is the distance from the top of the waste to where a seal is created. In that correct? - What does the 90mm stand for? The diameter of the tray's waste? The technical drawings at the bottom of the page has no reference to 90mm - Would it fit into a 50mm waste hole? Again, no reference in the drawing.
Or this one: https://www.screwfix.com/p/mcalpine-shower-trap-chrome-effect-70mm/47945
Would it fit into a 50mm waste hole? I did notice that some traps are for 50mm and some are for 52mm holes (2" I assume).