Hey Dan, I was looking at getting some of these smaller wheel cylinders but I noticed Raybestos WC37696 and Wagner WC113704 both look to have a metric brake line inlet.
No, the WC37696 has 3/8"-24 brake line thread, though I do see where RockAuto incorrectly lists it as having 10mm. The WC113704 had 3/8"-24, too, but that no longer matters; it's obsolete/NLA.
(I installed my first set of WC37696s in an A-body almost three decades ago, and the car's original brake lines threaded right on in. That post I linked has been up almost that long, and nobody who's followed it has discovered metric threads on their new cylinders.)