If it is the stopper ball, it must have been the piece of line that attaches the clew of the mainsail to the top mainsheet block - encircling the boom. It is a loop of Dyneema with a stopper ball on one end.
String it up by taking the loop end through the eye on the clew around the boom, through the shackle on the top mainsheet block and around again. The loop then slides over the stopper ball. I guess the stopper balls were cracking under load (?).
The soft shackle on the Orbit maisheet blocks are on the bottom block. Mine did not seem to twist very well.
