Which one?

Eight-foot-two-by-four is correct

#2

I need twenty eight-foot two-by-four lengths (of wood) to repair my fence.
I need twenty eight-foot two-by-fours to repair my fence.

Both are now possible.

Thank you,
Hmm. I assumed that "two-by-four" cannot be placed as a noun. So, I guess "two-by-four" has plural 's because of twenty. Right?
But, I wondered how? It is somehow describing something with dimensions, and describing is the work of adjectives.
Would you please explain that?

Thank again

Anonymous Eight-foot-two-by-four is correct

It is not correct.

AnonymousEight-foot-two-by-four is correct.

No.

PaeezSo, I guess "two-by-four" is plural (s) [no apostrophe] because of twenty, right?

Yes. twenty two-by-fours = twenty pieces of lumber

Thank you, but how an adjective can work as a noun?

PaeezThank you, but how can an adjective can work as a noun?

What word is doing that?

He's being confused because we've "nounified" the adjectival phrase "two-by-four", which, strictly speaking, describes the dimensions of a piece of lumber.

CSnyderHe's being confused because we've "nounified" the adjectival phrase "two-by-four", which, strictly speaking, describes the dimensions of a piece of lumber.

Yep! I understood that in that case the adjectival phrase was nounified. I want to learn how and when we are able to do that thing! You know, in every language it is possible to use adjective/adjecti