Do I need hyphens? Should I use the indefinite article or zero article?
Answer
It is incorrect to write “a 5-mm-thick layer”. Rather, it should be written:
a 5 mm-thick layer
or, better,
a five millimeter-thick layer
5 mm-thick is a compound adjective formed from the adjectives 5 mm and thick, and it modifies layer. Consider:
- a 5-mm layer/a 5 mm layer
(as a matter of style, some writers don’t hyphenate numerals with letters)- a five-millimeter layer
- a thick layer
- a 5 mm-thick layer
Note that as a compound adjective in its own right, 5-mm/five-millimeter is hyphenated. When compounded again, though, the first hyphen is dropped: 5 mm-long/five millimeter-wide, etc.
Other similar compound adjectives can be found in contexts similar to the following:
- a five year-long period
- a two month-old movie
- a ten year-old boy
Review this article for more on compound adjectives.
Attribution
Source : Link , Question Author : Lena D , Answer Author : Jimi Oke
