Mirroring a 3d feature ?

I want to mirror a 3d feature with out mirroring the complete part? It can easily be done in ProE, so it must also be easy i mechanical desktop.
Thank yo for your help.

 

[svanels]

Slice the part, mirror what U need and use union to get the sliced pieces together again Steven van Els
SAvanEls@cq-link.sr