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I was trying to install a Shimano 600 bb into a frame, and it didn't fit right. Insufficient threads on the adj cup side, couldn't put the lockring on.
When I first got this frame & fork I measured the bb shell real quick with a pocket rule. It was less than 73, so it must be 68. Surely there is nothing wrong with this assumption.
Shout out to Sutherland's. It's full of useful info for people who are into (or dealing with?) old parts. There's some info on Sheldon's page, but it wasn't enough for me to figure out a fix.
Turns out 70mm shells wwith English/BSA threading exist, and they take a 5xx spindle, which I previously thought was reserved for "Italian Stuff".
Why am I seeing this on an old Japanese bike? Probably because Sugino were straight ripping other parts, and didn't realize they were copying the nonsense too?