I'm not sure why it would be so at your end of the world, but have you considered a metric thread? Up here in Canada, where our leaders decided in a fit of insanity to go metric in 1976, we have to contend with that a lot. A 6mm bolt is 0.236"dia., the thread has a 1mm pitch, while the 5mm metric bolt is 0.197" dia., with a thread pitch of 0.8mm.