Thanks George,

I believe the hex heads predate the slotted screws though I really don't know either. As I received pictures during my research it seems to me the earlier Mach I's used the hex heads, but the number of subjects I had to compare was small. It should also be mentioned that there were very early ones, the first of the series I believe, that had red anodized cylinder muffs instead of green.

Anyway, if anyone has one with the hex head screws DON"T replace them, they are probably original. In fact is anyone has one with the hex heads and they'd like to part with it, let me know, I'd like to have that example as well, and condition is not and issue!