What’s the Difference Between Loctite 638 and 680?

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• 638 is specifically designed for metal-to-metal applications and may not be suitable for use on an O.D. rubber seal surface to metal housing.

  Loctite 638 would be preferred for faster cure time and higher strength, while Loctite 680 offers better flow properties and higher heat resistance. 680 may not be suitable for preventing metal roof screws from backing out. It is more effective for filling gaps up to 0.015 inches, making it challenging to achieve a small gap with sheet metal screws.

  I’ve written a more detailed analysis about Loctite 638 vs. 680, feel free to take a look.

  

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