Fastener library - best ways to define material?

Looking through a number of fastener libraries we have access to, I'm noticing that they handle material assignment differently. 

• No actual material assigned, just a density assigned to the generic
• Multiple materials assigned, but instead of adding the material to the family table they added the density. Which seems odd to me.
• The default load point PTC fastener lib has neither density or material assigned. 

So what would you do if you were designing a fastener library from scratch?

• Would you assign multiple materials, and then add the material to the family table so it can be selected?
• I suppose you could have a nested family table for a screw type, say socket head cap screw, then ask the user to pick the material next.
• Or you could put the material choice last after thread diameter & length and not nest the family table.

Looking for suggestions and a discussion to guide my thinking on what to do with our current libraries.