I'd gotten foal size they fit but, they don't fit. The cheeks don't go back quite far enough, yearling would be way to big & mini in the brand I use are hard to find.
Pippin was doubtful at first, where he came from he'd most likely never worn one. He's pretty game & was willing to try though. Plus he does trust me & cookies never hurt.
Once on however, Merlin took one look at this strange "new horse", got all stalliony & charged. Sorry no pix! Once he realized it wasn't a "new horse" in his pasture.
Next up Merlin, where he came from I'd fully anticipated masks were standard gear. Easy peasy, not thrilled but, no biggy.
UNTIL, Pippin decided he then had to chase the "new horse!"
Oh, after they of course helped one another out of their masks.