Support cords from the top of the center post to the ends of the spreader arms establish and hold the beam in an inverted umbrella shape. Two other cords between spreader arms 1 and 6 on the front of the beam also play a role in maintaining the hexagonal beam shape. The cords, except for the short cord, are all exactly alike. They are each 128 inches long and have S hooks on the ends for attachment to the center post and the ends of the spreader arms.
Measure and cut seven cords each 130 inches long.
2. Attach S hooks
Tie an S hook to the ends of each of the seven cords so that the total length when finished is 128 inches including the two hooks on the ends. The photos show use of aluminum sleeves but knots work just as well.
3. Make a small cord
Measure and cut a small cord 89 inches long and tie a #6 hose clamp to each end. The finished length is not critical.
The cords will supply all the tension needed to pull the spreader arms into shape so that it is not at all necessary or desirable to have the wires under any tension except for their own weight. The tension on the cords is well under ten pounds so the use of “no stretch” Kevlar cords covered with Dacron is completely adequate. Dacron cord is fine too but stretches more so when measuring for length, the cord should be pulled very firmly to a stretched state when measured.
You can buy already assembled Kevlar support cords here.