These predrilled hexagonal 6-arm PVC connectors for ½ inch pipe are injection molded with a 10 degree inward curvature. Each arm has exactly one inch of sleeve room for the inserted pipe, and a bolt hole drilled 1/2" from the end of each arm. You have the option of glue/welding the hubs to the pvc pipe, or fastening them together with nuts and bolts. The latter makes for easy disassembly/reassembly.
The center of each hub is solid PVC (that's where hardcore comes from), which means you can screw into it from the top or bottom, depending on how you want to attach a covering to your dome.
When calculating the lengths of pipes, please notice that we've already taken into consideration the 1.14 inches from the center of the hub to the beginning of the sleeve-fit portion for each arm. If you use our dome calculator, it's already part of the formula. If you use other dome calculators, most of them don't consider using hubs, but measure from vertex to vertex (centerpoint to centerpoint), so be sure to subtract 2.28 inches (2 X 1.14") from the lengths of those calculations so that your pipes aren't too long. If you're totally confused now, think of it this way: the hub itself adds just over an inch to each end of the pipes when they're connected - from the end of the pipe to the center of the hub. Since both ends of the pipes go into hubs, you need to subtract 2.28 inches from the length of each pipe if your calculator is measuring centerpoint to centerpoint for the strut lengths.