I have Inventor 11 (sp3)... hopefully get 2008 in a few months... but that doesn't particularly help me today. ;)

I have a small iAssembly, and I want to use some Hex Socket Head Cap Screws in it.  Thing is, I can't seem to change the size of the screws for different iAssemblies... say, #8-32 x 9/16 on two assemblies, and 1/4-20 x 5/8 on the third.  I of course use the "Table Replace" option to choose different iParts for each assembly... how do I do this for content center parts?  Or, do I have to create my own screw as an iPart to accomplish this?

Thanks!