Axles are typically 9 or 10mm thread.
Bicycle Bearings are almost universally imperial sized - 5/32", 3/16", 1/4", not metric. Rear hubs are normally 1/4".

The important parts of cones are the bearing race profiles and diameters.

Doesn't really matter what side you take it apart from, just that you leave one side tight to keep the length adjustment. On a solid axle it matters even less as you don't need the length adjust to be so close. YOu may want to work with a shop to match up cones.

https://wheelsmfg.com/products/hub-parts.html?p=2