what the heck is this?!

[Pulsar]

Stainless steel?
Why? Antifreeze has a pile of anti-corrosion stuff in it.
Brass would last longer in the area those have to live in anyway, you do know that salt is bad for stainless right?
Every one i have seen out of an engine is brass.

Well, I can attest a couple million myself with stainless. No idea what manufacturer uses brass.

Pipe plugs are made of different material (differentiation: pipe plugs have threads and are run in with a torque gun, cup plugs are pounded / hydraulically installed).

 

[Slacker]

Never used one but always kept these in mind just in case.

 

[MedicBob]

If it isn't actively leaking, leave it alone. They are a pain to replace. If you do get the hole in the block spotless, but do not make it bigger. Hone it just enough to clean the old sealant.

 

[slag]

I've replaced steel ones before. Can be a pita, have to be extra careful to not score the block with the tool when you remove them. Usually you can drill a hole in the middle, insert a screw and yank them out after loosening them with a screwdriver and hammer.

I'd tend to leave it alone if it were me.

 

[Homerboy]

The current plan of attack is ignoring it (until it becomes "a problem")

 

[jaha2000]

Great approach...