These 4-arm ABS connectors are made to be used on the base of a geodesic dome and fit both 1" and 1 1/2" schedule 40 pvc pipe. They have been injection molded with a 12 degree inward curvature. Each arm has exactly one inch of sleeve room for the inserted pipe. The center is solid ABS, so you can screw your cover into it from the top or bottom, depending on what kind of cover you choose. Although each arm has been designed to resist over 200 pounds of angular force, domes built using these hubs are not for climbing. These hubs have holes in them for bolts, although you can also glue the pipe to the hubs for extra strength and stability. This hub is perfectly designed for 3V domes and spheres, because of the 12 degree (per arm) curvature. If you use a strut-length calculator (based on vertex-to-vertex measurements), make sure that you deduct 4 inches from the centerpoint-to-centerpoint lengths, otherwise your pipes will be too long. The 4 inches equates to the width of the hub that is in addition to the strut length.

The hubs come in white ABS plastic, which matches the schedule 40 pipe. There is a small alignment arrow molded into each arm to help you line up your drilling points on the top side of each hub. The holes for the bolts are tapered, so the heads of the bolts will sit flush with the top of the hub (for 1"pipe).