The Right Bit for my pony..?

Well my pony uses a 4.5" tom thumb broken bit(looks like a snaffle, but its a tom thumb). and listens very unbelievably well. I bought him a full cheek snaffle and i have no control. When I showed him english, he galloped around the arena. every time I put pressure contained by the bit he would break, but if i put leg on him, he takes off. I am working next to him and he is still green, but what bit would work for him? I have tried a Kimberwick and I think he did not like it too much (it be a snaffle one). So what do you think? Oh and it has to be approved by 4 h laws. Please assist!! I think a pelham would be to strong, but i could be wrong. And whats the difference between a tom thumb pelham and a western tom thumb? Would a Tom Thumb Pelham work on him if he likes the regular tom thumb?? please serve asap :)
Answers:    i only use an regauler tom tumb for my lessons and the horses seam to lithen to it very capably im not sure about 4h seam as i only do module and trail rides

the western tom thum i belive its stronger so u only use the slighter touch and not a pull the full check can be very anooying and it can rub ur beter to use ur normla tom thumb or and eggbut for ur english
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