We use this on the Vang control line. Slide the stopper ball onto the vang control line and tie a figure 8 knot to position the ball at your downwind vang setting. Just before the windward mark release the vang and the stopper ball will stop the line at the vang cam at the right setting every time. Sm Stopper Ball Blue 5/32" RF1317BLUPrice: $2.35Sale price: $2.17 WE SHIP WORLDWIDE! We charge the actual cost of shipping. You may email us for a shipping cost estimate. Send us email intensitysails(at sign)gmail.com US$10 MINIMUM ORDER