I had 2 equal parts in an assembly, and wanted to move them freely and symetrically around a mid-plane. I did not find a suitable constraint in Alibre, and therefore combined 2 planes and an axis in order to obtain what I wanted. It works very well, here is how: 1) Place the 2 parts into the assembly and constrain them linearly so they can move freely and in line. Position the parts symetrically (approx. only - not accurate) on each side of an origin plane. (picture 1) 2) Insert a plane touching two edges on the parts (picture 2) 3) Insert another plane touching the opposite edges (picture 3) 4) Insert an axis in the crossing of these two planes (picture 4) 5) Constrain the inserted axis to the origin plane Now the parts will move freely and always symetrically around the origin plane. If the inserted planes/axis are hidden it looks like a genuine Alibre constraint. Of course you can make this movement around any plane, I use the origin plane just for easier explanation. Perhaps could it be added to existing constraints in the constraint window?