I have a thought on why certain models/sizes just aren't showing up. Back when, only rarely did fellas buy the etc. tool in sets. Sure some did, but with money as tight as it was, I feel a lot of guys only spent money on what they had to have. When standard size bolts were in use exclusively, manifold bolts, starter bolts on a variety of engines probably only came in 3-4 sizes. Maybe on aircraft, marine engines there were 3-4 more sizes, so if a jobber kept a full supply on the wall, only 3 sizes regularly went out the door. Anyone agree on this?