One of the handles snapped off a Y valve at the garden and I finally got around to an autopsy:
That’s using a 24 tpi bandsaw blade, which doesn’t cut nearly as smoothly as a fancy diamond saw, but seems good enough for the purpose. Most of the ripply shading on the cut plane comes from specular reflections; it’s pot metal all the way through and cuts to a high shine.
A closeup shows more detail around the (now hemispheric) ball valve:
You can see faint straight lines just inside the hose threads, which gives a hint of what’s to come.
Pry out the sectioned ball and dislodge the O-ring from the now-obvious insert:
Gently squish the threads in the bench vise to pop out the insert:
If lives depended on it, one could dismantle and repair the valve without recourse to a bandsaw, but …