They're obviously not all interchangeable, because I've tried. But I've never specifically looked for them so I don't know what the standard sizes are. I could measure a few, I suppose, but it's easier to ask here and drink my beer.

I've really had no preference as far as materials go up until now, except that plastic is better for my teeth when I'm on the tractor, but I'll be working outdoors for the next several months in the frozen northeast. I learned long ago not to put frozen metal near my mouth.
Who makes/sells different tips of different materials for specific tanks?