Common abbreviations use the same form for singular and plural.
in.—inch, inches
ft.—foot, feet
oz.—ounce, ounces
rpm—rotations per minute, not rpms
A few abbreviations, usually those preceding a number, require an s to form plurals.
lbs. <BH&G uses lb. for plural also>
pgs.
figs.
yds.
Nos.
CDs
Abbreviations
Capitalization
Company Names
Dates and Times
Degrees and Certifications
Periods
Plurals
Spaces