Google "internal pipe wrench" and the truth will be revealed. :)

There it is!

Thank you.

That’s good Info. I feel it's luck I have not needed one in my
home and automotive handyman work. I
have gotten by with extractors, external pipe wrenches, channel locks and vise
grips.

Were they basically designed
for chrome, brass or delicate pipe?

I have a couple probably bigger ones that are for galvanized pipe. I must have needed one of them once. I would guess the above ones would work for any pipe, but one would guess they would mostly be brass these days.