It’s not very often you call at a pub and they have all the different sizes side by side. Thought I would take a picture. There are a couple of sizes smaller that are missing 20ltr and 30ltr and of course the hogs head (54 gal) for example.
But how small or how big do you want to go, a 36 is big enough to throw around, if you can that is, it probably wont be around for much longer. It has been a health and safety issue for a long time.