A 3D/Polyline Solid can easily be added to the User Catalog in X15 and newer versions using the Add to Library edit tool. However, in X14 and prior versions, a 3D/Polyline Solid must first be converted to an architectural block before it can be added to the User Catalog in the library browser.
Many Architectural Blocks in the Library Browser can be exploded into their individual pieces, then modified, blocked back together, and added to your User Catalog.
