[jhautz]

Brian you are right about that. I wouldnt consider the reduceres as a permanent solution. I bought mine when I first got my 1940/7 and didn't know what gearing i was going to need. I used the bore reducer with my 5mm pinions until I figured out what the right gearing was and then I bought the correct pinion gears with the 4mm bore.

Plus in a pinch if you loose your pinion and need to run a regular 5mm pinon to get you through the day, they are nice to have.