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Which is correct:
- For interest sake
- For interest's sake
- For interest sakes
- For interest's sakes
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Only #2.
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What's the context?
- For interest sake
- For interest's sake
- For interest sakes
- For interest's sakes

You can also say

eg I read my dictionary for interest.

eg I read my atlas out of my interest in geography.

Students: We have free audio pronunciation exercises.
Comments  
anonymousinterest's sake
 Clive's reply was promoted to an answer.
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For interest's sake
For interest sake