Thanks everyone, he spends hours applying that eyeliner
To answer a few questions:
His bit was given to me by a friend, it isn't rubber, its plastic over metal so its solid. It's 3" (or 3.5" I can't remember) with loose rings through it. She had it from a pony she had many moons ago but I've seen them on ebay, I think they're classed as in-hand bits.
My roller is Mark Todd and that is cob/full size (LOL I know). If you look closely you'll see that the girth straps are looped up through the rings!!!!!! It has a 24" girth on too - it will fit him without "modification" when I find an 8" girth
I already had it from lungeing my big boys so just modified it to fit the wee one
I think if you got it in pony and bought a small cub girth, it would fit the littlest ones. I can get my arms right round Truffles' tummy so he's only little
Full cheeks are often the way forward with youngsters - the cheek helps to reinforce the aid. Basically, we spent all their babyhood teaching them to yield away from pressure, and then under saddle we put a little pressure on the side of the mouth and expect them to turn towards it (yes obviously we use legs too, but the little mouth pressure is still there). The cheek puts a bit of pressure on the opposite side, just like giving a little push to say "go that way please". They're good for anything green under saddle