When to use full stops with abbreviations
The rules around punctuation with abbreviations are as follows.
Abbreviations of first letters
When a word is abbreviated after the first few letters, the traditional rule is to put a full stop after the abbreviation.
However, many writers no longer use a full stop with some common abbreviations, such as days of the week or months.
Abbreviations of first and last letters
When a word is shortened by using the first and last letters, you do not need a full stop.
Mr Dr Pty
I notice that many US writers use full stops with Dr. and Mr. so maybe the US guidelines are different.
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