All hex nuts and hex headed bolts come from hex bar stock. One of my friends has a machine shop with a number of automatic screw machines and has hex bar drop offs from 3/16 to 2.5 inches in brass, aluminum, steel, and stainless. The drop off is the last bit of bar that won't chuck up in the collet and feed so it is scrap. I get several of each size from him and use my lathe to make bolts not readily available from most fastener places; stuff like some convertible top bolts or bolts with a long shank and just a few threads on the end, or something as common as hood arm shoulder bolts.
