These custom designed hubs become the base connectors at the ground level for all the 1/2" PVC domes. They’re injection molded with a 10 degree inward curvature.
Each arm has exactly one inch of sleeve room for the inserted pipe. All the hubs have a predrilled bolt hole 1/2" into each arm. You have the option of either gluing the pipes into the hubs, or securing them with nuts and bolts. These are included in both the Basic Kits and the Full Kits.
When you start to build your groundbase level, make sure you place the flat side of the 4-Star hub down, with the two open arms pointed straight up, and the curvature facing inward. If you are using a non-Sonostar calculator, be sure to subtract 2.28 inches from vertex to vertex.
The center is solid PVC (hardcore), which means you can screw into it from the top or bottom, depending on how you want to attach a covering to your dome.