Punctuation in abbreviations

People are often uncertain about whether or not to use periods in abbreviations. Here are some guidelines:

1.  In both American and British English, if you are using initial letters to represent words, you don’t normally need to put a period after    them:

 

2. In American English, however, it is common to use periods as an alternative style for certain abbreviations, in particular: 

3. If an abbreviation consists of the first and last letters of a word, the American rule is to include a period at the end:

5. If the abbreviation consists only of the first part of a word, then you should put a period at the end: