We recommend using these attachments for every hub at the top of the first tier. Use the Fabric Clips for the struts on the equator.
For the 10', 13' and 16' 2v domes that have 10 hubs at the top of the first tier, you will need 20 test caps, and 10 carriage bolts.
For the 24' 3v dome that have 15 hubs at the top of the first tier, you will need 30 test caps, and 15 carriage bolts. If you need to tighten your plastic, you may want to add more test cap connections at the top of the second tier as well.
This technique works best with a single layer of plastic, but one of our customers, Bill Randazzo, has shown us it is possible to attach a layer of plastic to both the inside and outside of the dome using test cap covers. You can see Bill's pictures here. Our hats are off to "Mohawk Bill", who is one awesome dome builder.
By using Bill's technique, you would save money over buying the Dual Ring Hubs, and we support economical solutions.