A PS on that...
Some parts catalogs have lengthy "Standard Parts" sections in the back, others very brief. There is also a Ford Standard Parts catalog with full listings...mine is I think about 1946. The suffixes like the "s" above call out the finish, plain steel, cad or nickel, etc. The catalog in my office doesn't have that info.
The standard parts numbers are, I believe, auto industry standards, not just Ford. If I am correct, you could go into a Chevy dealer today and perhaps get a bolt the right configuration...though I am sure non metric stuff is disappearing fast, AND you would be getting a modern equivalent with modern standard head thickness and configuration.
In the Ford catalog, standard parts are those things that are available through normal hardware channels.
If a bolt or whatever has special characteristics peculiar to its Ford use, special shape, special heat treatment, whatever, it will carry a Ford part number. Your head studs, for instance, carry a Ford PN in the engine series, while the nuts on them are standard parts. You can get a usable stud at the hardware store, but it won't snug into the Ford recess properly so it stands straight and it probably has different toughening standards in its heat treat.
