The variable CenterOfMass provides the position and orientation of the center of the mass related to the mounting point using a 3DFrameType. X, Y, Z define the position of the center of gravity relative to the mounting point coordinate system. A, B, C define the orientation of the principal axes of inertia relative to the mounting point coordinate system. Orientation A, B, C can be "0" for systems which do not need these values.
3DFrameType and 3DFrame are defined in OPC 10001-11 (SpatialTypes).
If the instance of the LoadType describes the flange load of a motion device the mounting point coordinate system is the flange coordinate system. If the instance of the LoadType describes an additional load of an axis the mounting point coordinate system is vendor specific and it is up to the vendor to model this coordinate system.