Alright, you guys got my lazy ass off the coach! I just measured a front drum @ 4.998" and rear drum @ 5.003". So, lets call them 5", which is 127mm. I put a pair of worn shoes in a backing plate and measured 121mm. I say the 125mm pair is probably more correct. I will have to look back, but someone posted a minibike brake a while back that they use.