Sometimes a noun phrase is used as an adjective (a single concept) to modify another noun, and to turn the phrase into an adjective, one or more hyphens are used. These are called compound modifiers.
Examples with one hyphen:
Examples with two and three hyphens:
Fit-for-purpose tubing design
Now, if the modifier is in the predicate and does not precede the noun it modifies, then you do not use any hyphens. The hyphens are only used for clarity so the reader can figure out which noun is the subject of the sentence.
Examples without one hyphen:
The author was well known.
The street runs one way.
Examples without two and three hyphens:
The schedule is up to date.
She kept track of her expenses day to day.
This software program is state of the art.
And here is the funny typo of the day:
Fir-for-purpose tubing design
I guess this particular custom tubing design is specially made from hollowed fir tree trunks!
Famous Day-to-Day Quote:
“Being in control of your life and having realistic expectations about your day-to-day challenges are the keys to stress management, which is perhaps the most important ingredient to living a happy, healthy, and rewarding life.”
– Marilu Henner, American actress (TV series Taxi), b. 1952