Punctuation in abbreviations

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

1. In both British and American English, if you are using initial (i.e. first) letters to represent words, you don’t normally need to put a full stop after    them:

 

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

3. If an abbreviation consists of the first and last letters of a word, you don’t need to use a full stop at the end:

4. If the abbreviation consists only of the first part of a word, then you should put a full stop at the end: