A couple of questions about the design of NEMA plugs:
What is the purpose of the small holes near the tips of the hot and neutral blades in most, but not all, of the smaller straight blade plugs, e.g. 1-15, 5-15, 6-15, 7-15, 5-20, 6-20 etc? There's nothing in the receptacle which locates in them, and they reduce both the cross-sectional area and the surface contact area at just the point where the blades make contact with the receptacle. They don't seem to serve any useful purpose, and some plugs don't have them. Are they there for some historical reason? Wouldn't eliminating them provide better contact?
The ground pin on moulded-on 5-15 plugs is usually a thin metal tube, with the end domed over to form a test tube type shape. On re- wireable plugs, and on the larger ones, it's usually made from a flat strip of brass bent into a 'U' shape. Why the difference? Wouldn't a better contact be made if they wee all the same shape, rather than the contacts in the receptacle having to work with both shapes? Come to that, why not use a simple solid round or rectangular bar, as most other plugs in the world, except side contact types such as BS196-1961 and German Schuko ones do?