I see these for sale in hardware stores.

Most of them are Nema 1-15 caps, though (made either by Eagle Electric or Gem Electric).

Why make the pins out of steel instead of copper or brass?

Usually the pins wind up rusting after a few years in service, particularly when it's on something that gets constantly plugged and unplugged (and the zinc or copper plating rubs off the steel blade).

I've run across a number of such rusted attachment plugs on old lamps and other appliances

Normally I avoid them and choose copper bladed caps unless I have no choice, but it always intrigued me.

Also steel isn't that good a conductor, and don't you have some sort of reaction when you connect things like zinc/steel and copper, or is that only with aluminium?

Hey Swen:
My best guess, and IMHO:
Copper prongs on plugs would be to "soft", and would be an additional cost factor in mfg. Brass was/is used, also brass plating, and nickle plating on whatever base metal the mfg uses.

Im'm not a metalurgist, but I don't think there is a problem with any of the dissimilar metals you mentioned.

Also, you stated that you have seen "rusted" attachment plugs, I can't recall ever coming across any. I'm not doubting your comment, but are the ones you found a "factory" plug, or an aftermarket plug?; and are they from the USA??
John

I was referring normally to replacement (aftermarket) caps.

Most factory molded plugs are made of what seems to be nickel-plated brass (it definitely isn't steel because it's not magnetic). On a side note, I have a small GE alarm clock (probably 1960s or 70s vintage) where the blades on the plug are aluminium!!

The rusted prongs on cord caps I've run across are American.

Joe Tedesco once posted a picture of a stump of lamp cord with one of those round rubber replacement caps and the pins were visibly rusted.

I haven't been able to find the picture (perhaps it was deleted). Maybe Joe can repost it?

Don't have a digital camera, or I would take a pic of one or two of such old ones I've removed that I still have lying around at home.

I know this really isn't about the material the plugs are made of, but does anyone know why plugs have those holes on the very ends of them?


Lee