I'm not sure the Cashel mask comes in anything but Mini and pony size. Pony size is actually a small horse size mask, I forget if it is labelled weanling or yearling. But, unless your B size Mini has a very large head, don't let anyone talk you into buying the pony size Cashel mask! I needed one for a 40" pony--I told them that she has a smaller head and at the time wore a Mini L size halter. The gal either didn't listen or simply didn't have a clue--she told me to order the pony size one. I did. By the time I bought the mask & paid for shipping to Canada, I had a mask that cost me over $50 and IT DIDN'T FIT! The velcro under the throat wouldn't tighten up quite enough to make the mask fit well enough to stay on for any length of time, and the nose piece hangs well below the end of the pony's nose. So, my very expensive mask has sat unused in the drawer for several years now. That particular pony has grown some & now wears a Mini XL size halter, and that mask still wouldn't fit her. I'm honestly not sure that it would even fit Tim, my biggest Shetland, he's 44" but still doesn't have a real big head--I'll have to try it on him.
I bought a Farnam mini horse size mask for that pony mare & it fits her great even now. It does have room to adjust out to fit a bigger head, so I suspect that it would also fit the biggest of my B Minis. Mine doesn't have the ears on it as I needed it to prevent sunburn on her face & so didn't need ears on the mask, but I think Farnam does have the masks with ears as well. That is the mask I would recommend--and I would suspect that the regular Mini size would work for you--the Farnam mask has held up very well for me & it stays on & in place really well.
