Valve stems are made of stainless steel threaded rod. Mine were made of salvaged 10-32 bolts. 8-18, the generic stainless for screws, is a good grade of stainless for machining. You of course could use brass or threaded bronze rod if you like.
I used a threaded bushing to protect the threads mounting that in a collet. I cut the shaft size to 1/8 for .625” long. I decided this was a good time to drill and tap for the bolt that retains the handle. If I should break off a tap then I would not have a lot invested in the part yet. Maybe drilling and threading should be the first step.
I then turned the valve stem around and cut the unthreaded section at .156 at leaving a .25 long threaded section. Next the 60 degree angle on the end. I got away with using an angled cutter rather than using the compound. I held it by the threaded portion in the bushing to keep it as stiff as possible.