It's called a wheel stud or lug. The part proper is like two bucks and can just be banged out with a hammer, but I think on your axle it's a pain to get to.
That's not catastrophic as long as the other five nuts are properly tightened. However, with a busted stud, I'd question if the others have been mistreated (either too tight or too loose) and that IS bad. It is a good idea to own a torque wrench to properly check the lug nut tightness.
If memory serves, on half-ton axles you remove the wheel and then slip the brake drum off. At that point you have access to the end of the axle shaft, which is a flat round plate about, I donno, six inches in diameter with the studs pressed in.
Ideally you'd press it in and out with a C-clamp, though in a pinch it could be removed with a sledge. Also, though you're not supposed to, you can draw the new one in with an impact. You put a few washers of larger ID than the stud knurls under a lugnut and brrrp.
ANYWAY, it could be a fun way for you learn about your truck, or if you prefer, any tire shop should be able to do it for you fairly quick and cheap. Years ago I recall it being ten bucks, though I'm presuming the rate has gone up.
Either way, do verify that ALL the lug nuts are properly tightened.
-- A