[quote]ORIGINAL: RRyan

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.

Hi Randy,
The Sept 1954 Aerom has Warring's test of the 1st model Mach 1 Diesel, released in 1953. It has green fins and cheesehead screws. It would seem that the red fin engine was released sometime in 1954.
regards
David Owen