> When a metric value is used as a one-thought modifier before a noun, hyphenating the quantity is not necessary. However, if a hyphen is used, write out the name of the metric quantity with the hyphen between the numeral and the quantity. For example:
a 2-liter bottle, NOT a 2-L bottle;
a 100-meter relay, NOT a 100-m relay;
35-millimeter film, NOT 35-mm film