Step 5: Stand Connections
To connect these stands to our wooden arc we needed to buy 4 pipe flanges and 4 short pipe sections that where threaded on one end and were the right diameter and pitch to screw into the pipe flanges and also to accommodate the top tubular portion of our light stands. The spacing on these legs is not as important as the spacing of the cameras, so when you are deciding where to mount your flanges to the bottom side of the arc make sure that they are not interfering w/ the locations you plan to put the camera bolts. We had to drill and tap the pipe section (on the end opposite the thread) so we could use a set screw (a thumbscrew actually) to preload into the portion of the light stand that fits inside the pipe section. This allowed us to make a more secure connection between the platform and the light stands. Here is a drill and tap chart that will help you decide what size drill to use in order to create a nice tap.
(see the photo notes for more details on how to do this. Its dumb simple and easy to pictorially depict)
Once you are ready, you can drill your mounting holes and screw the flanges into place. Screw in your pipe section