I am helping/teaching a friend to overhaul his bike which is a Batavus Monte Carlo (No idea on the date). My question to all the Batavus experts is: What is the Bottom Bracket threading? I don't want to remove the cotters and find that I don't have a corresponding bottom bracket to replace it with. Thank you for your help and information.

.... uh, I have the same issue as this guy. Anyone know what kind of threading I will find on a Batavus Monte Carlo, early to mid seventies vintage? Thanks in advance.

Not sure what your BB is like but there was a thread several years ago concerning a rather unique Batavus BB. Maybe this info would apply to your bike? Anyhow, it also states that the Batavus staff is very responsive so dropping them a line might be in order as well?
https://www.bikeforums.net/classic-vi...moving-bb.html

I had a '75 Batavus Tour de l'Europe way way back when, and my memory is that it took a British BB. Mine was from the year they switched over to a Sugino Maxy 3-pin crankset. It was the same bike but with QR, large-flange hubs and chrome fork socks.

no experience of Monte Carlo model but the Batavus machines have worked on from this time had bsc/iso thread shells of 70-71mm width.