How to rotate or snap object parallel to specific face of another object? I imported object from another file (bended detail), it appeared slightly rotated. So now i need to rotate it thus faces indicated with red arrows would be paralleled (and to the flat).

attached file https://blend-exchange.giantcowfilms.com/b/KadW0M4l



I've found many tutorials about snapping. The most important information from them is that face snapping works with normals. And this info didn't helped me anyway =) None of them provide necessary result. 

It's either snap the detail to flat by pivot point as it is expected without rotation enabled:



or rotate it in a ridiculous way:
As @Sanbaldo mentioned in comment section, we can use Measurement tool to determine angle between faces and rotate source detail.  

In more complex situation this answer is available to solve this task:
https://blender.stackexchange.com/a/156469/87633

Thanks to @JachymMichal