After abbreviations.
Nicknames, _Sam_, _Tom_, etc., are not regarded as abbreviations.
The metric symbols are treated as abbreviations but the chemical symbols are not.

M.( metre) and mg.

(milligram) but H_{2} O and Na Cl.
Per cent is not regarded as an abbreviation.
The names of book sizes (12mo 16mo) are not regarded as abbreviations.
The period is now generally omitted in display matter after Running heads, Cut-in side-notes, Central head-lines, Box heads in tables, Signatures at the end of letters.
The period is omitted After Roman numerals, even though they have the value of ordinals.
After MS and similar symbols.
In technical matter, after the recognized abbreviations for linguistic epochs.

IE (Indo-European), MHG (Middle High German) and after titles of well-known publications indicated by initials such as AAAPS (Annals of the American Academy of Political Science).
When a parenthesis forms the end of a declarative sentence the period is placed outside the parenthesis, as in the preceding example.

A period is placed inside a parenthesis only in two cases.
1.