I followed the instructions last time on how to mirror my tube but when I tried it this time for my tube support rings, it didn’t work. It basically moved the duplicate to the other side but didn’t actually mirror it.
Here are the pics: http://imgur.com/a/PcKZR
Thank you all for helping me out!
The object has some rotation as you can see in the properties panel. Apply the object rotation before mirroring (Ctrl+A)
Thank you!
For future reference, also apply any scaling and make sure your object origin is in the middle.