A and B miniatures??

I am looking for a cart and harness for my miniature horse and the sellers are talking about A and B miniature horses that will fit the carts. But I don't know what an A and B miniature size is...I feel kinda stupid but I honestly don't know! Can someone explain to me what is the difference between an A miniature and a B miniature? Thanks!!
Also, if you know where I can get a cheap harness and cart at for my miniature (36 inch miniature) that would be awesome!! Thanks!

Yours sounds like a type B. The A minis are very short usually in the 20" ranges. Type B are more for cart pulling and up to 38" tall. Anything above 38" is considered a pony.

A size are under 34", B size are 34.25-38". Anything that grows over that size gets their papers pulled. Also, AMHA registered horses are always under 34".

Thanks, I am new to the land of minis so couldn't remember how tall the A's can be.