I ran into this problem when I wanted to convert two of my bikes to solid axles. It was pretty much an aesthetic pursuit, because I honestly couldn't say that there was anything wrong with the QR's. I ordered two 9x1 mm axles made by Wheels Manufacturing:

Wheels Manufacturing Hub Axles

My expectation was to switch my old cones to the new axles. Bike #1 , the cones wouldn't fit. I asked here, and learned that there are two 9 mm diameter threads. I tried Bike #2 , and the cones fit. The difference was probably European and Japanese, so I dug up another old Japanese hub and harvested its cones. In the end, everything fits.

An older Schwinn hub in my bin has the 5/16" axle.

A note about identifying the thread, 26 tpi is very close to 1 mm (25.4 tpi), so it might be hard to actually notice the difference unless you engage the nut or thread checker with several threads. Indeed, my 26 tpi cone went a few turns onto the 1 mm pitch axle before grinding to a halt, and the jam nut went on just fine. I may even have checked the threads with a jam nut before ordering the axles.

I'm guessing that the weird mixed English / metric threads arose from the availability of lathes and screw machines with English threading gears. Such a machine would let you chase English threads onto any diameter shaft, but metric threading required purchase of an additional set of gears. To this day, machinists will grumble if I ask for metric threads on a lathe job, which typically only crops up if I need a large fine pitch for some kind of lens or optical mount. Of course with taps and dies, no problem. But notice that 9x1 is not a widespread metric screw thread size.