The 
Fixed Constraint holds all the parts in the Move Parts list in their current location and orientation. Any following moves that list one of these parts as the "object" will force the "target" part to move instead. Generally, the first Mechanical move in a model should be a Fixed move. The part(s) listed will act as the base of the assembly. Parts may also be added to a Fixed move after they have been partially or fully constrained.
Procedure: Select the part(s) that will remain fixed in space. More than two parts can be listed for this type of move.
•Select the parts in the Move Parts Tab:
