It was used as support for the spar to help make the fin. At one time I had instructions for it's use, but I doubt I can find it now.

He had three sizes, small, medium, and large, they were used in all his kits depending on what size was required. The Hyper was two stage and had two sets of different size fins, for upper and lower stages.

CMR parts
 

Howard made quality parts, especially for the time frame with the recourses available. I still have a few egg capsules and ,(I think) , a set of these fins on a .903 body tube.