Importing Step Files w/zero mass

A connector manufacturer sent us a step files which have zero mass and appear to have been created with surfaces.  How can I import these as solid models, with the correct units, density and mass?  I also need these imported step files to appear correctly in the assembly model and drawing as if they are modeled.  Should the settings in the import settings windows be changed?  If so, which settings and what should they be changed to?  Thanks.