The mirror that came on my '46 is 6" round. I've been looking for a match to put on the passenger side for 5 years with no luck. Currently I'm running a pair of the standard five inch round mirrors and miss that extra inch. I'm going to get one of the convex 6" round mirrors and have my local glass shop swap in a flat mirror.
Before you destroy the one convex one on the passenger side, give it a test run. I did that on my '49 and '50, and it is amazing how the view is from that 5" convex mirror on the passenger side. That is the mirror which causes the most problems with blind spots. That convex mirror corrects that problem.
