While most mainsail working loads are fairly predicatable, it is easy to overlook "shock" loads that may be experienced by a traveler system. Jibing, for example can produce shock or impact loads well beyond normal sailing loads, as can the flogging of a boom and mainsail during reefing.
Schaefer End Control Blocks use Delrin™ Ball Bearing Sheaves and some use a Schaefer Fast Entry Cam Cleat for ultimate control. Various combinations are available to give you the purchase you need to tame your main or genoa traveler. Choose from numerous Schaefer Stand Up Spring adapters to allow you to plug your Schaefer Blocks into your traveler car. Cap off the sailboat tracks with Schaefer endstops made from UV treated Urethane to take the shock loads possible from your system.