millimeter, mm

Abbreviated mm, no period.

In text, usually spelled out as a noun or adjective, although may be abbreviated as an adjective in some

standard uses:

a caterpillar 25 millimeters long

a 10-millimeter-wide line

but 16-mm film

7.7-mm shell

In photographic data, film and lens sizes are often written without a hyphen:

35mm film

200mm zoom

Either style is accepted as long as it is consistent.