Why be ordinary? I think this is a good avenue for expansion. We haven't seen any improvement in these critters compared with say, spark plug wires.

The heck with steel, or brass. C'mon fellas, think outside the box! Exotic, rare-earth minerals are where it's at. Maybe a Vanadium-Titanium-Neodymium alloy, cryogenically treated and forged in alignment with magnetic North (NOT grid North).

I've used those expandable plugs numerous times and find they work quite well. My Hemi engine had three piece stainless plugs with an O ring. ALL of them were leaking! I replace them with the expansion plugs.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

I use  papco 1/3/4 part #263-612 expansion plugs. just clean the car plug hole ,install  tighten the bolt to expand the rubber. cheap and easy
i 

When I first got my TBird, I was driving down the road one day.   I jumped on the gas in first gear.  When I shifted into 2nd, a cloud of smoke came out from under the hood.  I pulled off the road into a parking lot.  The motor was still running.  I popped the hood to see what had happened.  One of the freeze plugs had blown out and was laying on the frame rail looking back at me.   I don't think the material is as important as how you install them.  

If using brass, you need to BRASSO them every so often -

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...that doesn't mean it was necessarily a good idea. In accounting, there used to be a term called the "Mill" which is 1/1000 of a dollar. If you pay property tax you already know about millage rates based on per $1000 value.

If the beancounters could save 1/4 cent on a part or gee-gaw, that was a big deal. Ain't corporations and horses built by committee grand?

factory used steel.

Cork.

"FREE SAMPLE"

I have no idea, I just figured somebody has to take the other side of the equation.

I’m inclined to use brass, especially if the engine is in the car and getting to it is difficult. It’s a little softer to drive in, or so it seemed. Either way I use a non hardening sealer and clean the block as best I can. On an engine stand with a boiled block, either steel or brass. I think brass is more forgiving of lack of maintenance (proper mix of anti freeze and changed as required), but if you're taking proper care, steel is fine.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ