Tube valve sizes!!!

Life used to be simple……….or maybe it was me. Anyways had a 7.50 x 16 tyre in shed so needing it for my trailer. Easy, phone up local farm supplier and get a couple of tubes. Oooh no, not that easy now is it? Do I want TR13, a TR15, aTR6 TR7 etc. Well I had a TR7 at one point but it was only used for sprints and hillclimbs and breaking down. Wouldn't have fitted in a tyre.
So anyway, not got one ordered yet coz don’t know which to get. Any suggestions?

If it is old style then most likely TR15. The TR13 is smaller diameter, like a standard tubeless rim size.
The others are mainly bent or bolt on.

If there is a huge difference in price you can get little plastic collars that allow you to fit a tr13 tube valve into tr15 rim. But it is just a case of measuring the diameter of the valve hole, standard land rover rims are tr15.