Originally Posted by dddd

Firstly, just for reference, JIS spindles measure a very consistent 12.90mm (measured 3mm from the end), including Dura-Ace.

I measure Campag's newer cartridge bb's as all having a very consistent taper width of about 12.70mm (measured exactly 3mm from the end).

I have earlier Campag spindles from the 70's and 80's, lots of them, however these vary quite a bit.

Most of these Nuovo-era spindles measure 12.70mm, just like the later ones.
About a third of them are in the 12.74-12.79mm range, however.

Older Campag-compatible Sugino Mighty spindles are 12.71mm.

Older Campag-compatible Specialized(!) spindles are 12.73 to 12.76mm (odd since they were likely made by Sugino, but could have been made to spec).

Stronglight Spindles from the 1970's might have been "ISO", but are the smallest, in the 12.64-12.67mm range.

A Suntour 112mm "BB-91" spindle from 1991 (dated HC) measures only 12.65mm (another Sugino-made part).

Again, all these measures are relative to a consistent JIS dimension of 12.90mm.

Lastly, I have one (1) Campag spindle (pretty old I'd say) that measures 12.9mm, but this is an anomaly I won't consider.
And one (1) Dura-Ace spindle 7400 here (again, too odd to count) actually measures about 12.99mm.
I have to consider that these lone two oddball-sized spindles might have become distorted, possibly from over-tightening, wherein the bolt's threads have perhaps forced the flats apart(?).

I've measured many different kinds of Dura-Ace spindles, and all appear to be JIS. A couple of the pre-7400 examples measured just a few thou on the small side of 12.90, but which would affect spindle insertion by well less than 1mm.

By my specific experimental measurements, each 0.1mm difference in tapered spindle width affects the insertion in the crankarm by 1.4mm.
I measured insertion depth into a locked caliper at two different settings, thus using a .5mm width difference to observe a roughly 7mm difference in insertion. (Thus, a ratio of width/insertion of 1:14)

Using mathematics, the cotangent (Y/X) of 4 degrees is 14.3, validating my previous measurements on a spindle with opposing 2-degree tapers.

It is sometimes the case that a well-used crankarm may have an expanded square taper bore.
Thus, older Campag cranks sometimes will take particularly well to JIS taper dimensions.