Microscope ring lights - One standard size? Or some sizes fits some...

[Skimask]

Are the ring lights for microscopes pretty much standardized or is it a crap shoot?  e.g. can you buy a generic one off ebay for product X and be fairly confident it'll fit on product Y?

[KJDS]

The simple answer is "mostly."

However I've not seen one that will fit my big Leica or any of the little non-zoom microscopes I've had, but every other one I've seen will fit any of the Optika, Motic, Zeiss, Amscope, Iroscope and countless others that I'd had.