Clipmodel
From The DarkMod Wiki
The clipmodel spawnarg specifies a file that is used to be as a collision model for the entity. This allows the CM to be in a different file than the model itself.
Preferable both should be in one file, though.
Example:
"model" "models/darkmod/weapons/broadhead.lwo" "clipmodel" "models/darkmod/weapons/broadhead_collision.ase"