This is an adapter for spools with a large center hole.
The scad is parametric, allowing various numbers of arms, different rod diameters, even an end-cap for trapping bearings or carefully sized mounting rods. You can also alter the height of the hub and tips.
The STL is sized for a spool with ID of 180mm, and a mounting rod of 16mm diameter.
*** UPDATED 26 March 20120 ***