*Thinnest and yet roughest. Not thick enough to be a barrier, and it can rub you raw to provide an entry point at the same time!

"Sealed" is also a vague suggestion with HVAC. Every ducting join, every piece of equipment, all of it leaks. I shudder to think how much heating/cooling is wasted that way.

It's more like, "I own 17 homes and it wasn't that hard to get that many. They must not be trying hard enough."

I kind of disagree with you, in that when I think about the standalone meanings of the words in each phrase, I think they do say the same thing.

The meaning of the words "You are welcome [to the help I gave you]" implies, to me, that there wasn't actually anything to offer thanks over. You're acknowledging their thanks, but telling them that they are welcome to take/use whatever it is you're talking about. [EDIT: normally when someone tells me I'm welcome to something, I feel less compelled to ask and thank in the future. "You're welcome to anything in the fridge", for example.]

It does not imply, to me, that I would appreciate them returning the favour. That might be implied meaning in the phrase, but it's definitely not what those words mean by themselves.

In any case, "You're welcome", "no problem", "no worries", etc... are all idioms that mean something different than what their individual words mean. The phrases as a whole carry a different meaning than the words themselves suggest.

Same. As it should be.

That analogy relies on the reader having any idea what wire EDM manufacturing is. ;) Not exactly an everyday topic.

Iron would be a terrible metal for coinage, since it would shed rust all over everything after being handled. Some coins might be cast from iron (if it's cheaper than alternatives, idk) but plated in other metals to prevent that.