I am still fighting with mirroring. Doesnt matter if I use Ctrl+M or Mirror modifier. My rivets go only in bad way. I mean I want them mirrored nicely along global axis to fit the opposite site. BUT the rivets are mirroring only along local transformations corresponding their base slope face.
Check the screenshots:

From pictures you can see that rivets want to be mirrored in the face direction they were created at. I used Snapping during transform (magnet icon) on the face and I had applied "Align rotation with the snapping target".
On the other faces it all worked fine, as you can ssee they are mirrored properly. But this last face which is not perpendicular doesn't work for me. What do I wrong? Thanks !
I must also say, that If I change GLobal transforamtion to local, or gimbal or whatever the result is still the same !
It behaves like it is a bug there?... Please help Karel