What model keg do I have?

Hello,
I have a various assortment of kegs, and I just want to know how I can tell which models are which. For example, Northern Brewer lists these various types under their Keg Plug types (follow above link):

Northern Brewer website said:

Type A plug assembly fits Firestone V, VI, Challenger and Super Challenger kegs. Type B fits Cornelius Spartan, Super Champion and 'R' kegs. Type C fits John Wood 85 and older Firestone Challenger kegs."

Click to expand...

So how do I know what model my kegs are/which plugs go with which kegs?

Thanks

Some of the kegs have the name stamped on the side - those are easy. Otherwise, you can remove the post and compare them with the pictures on the seller's website. Once you identify the post type, you can tell which of the poppits will fit.

I have one keg that no poppits fit at all, and I've tried all the ones that make sense. It's some crazy brand keg that nobody seems to have heard of. Just my luck. It may end up becoming a heat exchanger in the future.