I have an 88 Specialized Hardrock with 6 speed Suntour componentry, although I can't tell who is the manufacturer of the rear hub. I'd like to replace the solid rear axle with one that is QR compatible.

I know my choices for the diameter are 9.5mm (3/8"), or 10mm. The diameter measures 9.5mm at the threads but 9mm at the unthreaded portion. So I guess I need a 9.5mm, right?

That then leaves me to the threading, choices are 24tpi, 26tpi, or 1mm. How do I tell by looking? Or is it likely to be 26tpi, since that seems to be all I can find in 9.5mm?