Hanson, Skeletons constitute a pretty big topic, more than can be covered quickly in a Forum response. They have several uses and are especially helpful in assemblies with complex combinations and ranges of motion. They are what they sound like, a lightweight "hatrack" (often planes, curves, axes, and coordinate systems only) on which one can hang the "real" parts of an assembly, thus allowing much easier simulation of machine motion, assembly and interchange of components. They are also used to delineate "space claims", for example for a complex control chassis, packed with control boards and actuators. Look in Help and Tips and Techniques for more information. I would also reccommend an appropriate training course covering advanced assembly techniques. David
