G'day
Bon_Scott and
Mod BBI'm confident that BB states the best bet - the 45 had
unpainted fasteners.
At least that's what the vast amount of evidence suggests, and it has
better aesthetics - in my view

However, I would like to make a point about the major mower makers of the day.
Because the industry was determined by seasons - weather - OEMs would
use unskilled seasonal workers at peak season. Maybe, that's one reason -
and a touch-up was needed at assembly. Who knows?
The bolt on the Model 38 edger is hilarious.
Not sure who would put a spring washer under the head of a bolt!
I think there has been some contamination there.
I like this conversation because it goes to discussion about restorations.
I enclose two images below: one of a 45 with, I think, is a paint touch-up.
The other shows the correct Model 38 bolt and nut engine mounts.
Cheers------------------------
Jack