My 22 cents worth on this topic and probably going waaaay off topic........
I know Chris R's 302 was fitted w/ one 11mm stem; Chris' 302 was about as unmolested as a bike could be.
Cannot remember what Andy D's 175 had on it, seems 11mm stems. No doubt Chris R could add to this.
Cannot go by what 232 has. Late 2005, I purchased an early seat, blinkers and mirrors from the same seller in eastern Iowa. He alledged these parts were all "take offs" from a 69 CB750 he bought new June 1969. The condition of the parts would suggest they were "take offs." The pair of mirrors/stems were same condition, one was a 10mm stem, the other 11mm.
Just my theory, but I cannot imagine the assembly line (nor anyone else) measuring stem diameters for matching same diameter stems to be fitted to a bike, seems from what we know on this topic, early vins were fitted with 11mm stems........ For that matter, considering the mirrors were packed separately in the crate, not fitted to the crated bike, it's entirely probable mirrors were never fitted to the bike on the line, prior to crating..........
We can only speculate why the mirror manufacturer/supplier made initial prod.runs of 11mm stems, then changed to 10mm stems........
Considering all parts are manfactured to specifications from a blueprint, I'd guess the manufacturer or/and perhaps Honda knew stems were 11mm and the change to 10mm was deliberate............
Would speculate, when the supply of 11mm stems ran out, 10mm were supplied. And would further speculate the mirrors were received in batches from the mirror manufacturer, so when mirrors were pulled from their shipping carton, it's probable there was random and different diameter stems supplied to any given machine, i am guessing more likely on later vins, whereas early vins could have had both 11mm stems.
The more i think about this, makes no sense mirrors would be fitted on the assembly line,
then removed, to be wrapped in a parcel for crating to export.
More of my neurons are flashing....... NOW taking a look at the 11 page "CB750 Set-Up and Pre-Delivery Service Manual." (print date 69.6)
Contained in the "CB750 Set-Up and Pre-Delivery Service Manual," (print date 69.6)pictures and instructions in this manual clearly indicate what parts were NOT on the bike and were contained in a "parts carton (to be opened) to check the parts to make sure there are no missing parts or damage," after carton was removed from the opened crate. Those parts being, listed and numbered in the manual, "1. left front winker lamp, 2. tail/stop light assembly, 3. battery, 4. front fender, 5. seat, 6. gear change pedal, 7. clutch adjusting cover, 8. bolts and nuts, 9. foot rest, 10. rear view mirrors, step rubbers, Owner's manual, 11. front hose clip and 12. touch up paint." The picture of these parts taken from the crate clearly show all these parts (except mirrors) including two (mirror sized) boxes in plastic wrapping labled "CB750, attatchments, Honda."
Based on these pictures and instructions contained in this pre-delivery/set-up manual, the theory could hold up mirrors were not fitted on the assembly line, in preparation for crating/shipping the bike. Seems even more likely mirrors
(already individually boxed and never unboxed by Honda) were randonly and put in the "parts carton" to be sent along with the crated motorcycle.
An interesting aside, pictures and instructions in the manual reveal the bike being uncrated. Crated machines did not have handlebars fitted nor master cylinder fitted to handlebar. The gas tank, front wheel and brake caliper were not fitted as well as control cables not attatched to handlebar controls.
WHAT IF an uncrated sandcast exists...........
