1976 Super Le Tour 12.2. Frame built by Panasonic. What do you suppose the odds are that the headset is JIS rather than ISO, due to Panasonic being the manufacturer? I know, I know, the only way to find out for sure is to remove the cups and measure with calipers. But I would prefer to buy my new headset and do the removal and new installation all in one quick process, rather than tearing apart my daily rider to do the measurement, putting it back together, and then tearing it down again to install the new headset a week or two later.

I cannot find any specification documentation online to conclusively prove this to be JIS or ISO. The only thing people seem to obsess over on this bike and other Panasonic-framed Schwinns is that Schwinn insisted on installing a fork with a thicker-walled steerer tube, thus destroying the ability to easily access aftermarket stems without resorting to turning the stem down on a lathe (been there, done that to a Nitto stem).

So, gamblers, lay the odds on JIS versus ISO, and I will roll the dice and buy a new headset.