I am having some problems with mass propertis of some of my assemblies. The mass data for moments of inertia are not always give when i take the mass property of some assemblies. The assemblies consist of sub-assemblies and part files that are assemblies that have been saved out as .sldprt files. Also some of the parts have assigned weights to them not the calculated weights from the materials. Please if anyone can explain why the moments are not always there it would help greatly.