When control blocks are not used, add endstops to traveler track to absrob shock loads, and keep the car on the track. When end control blocks are used, use trim caps to finish track ends. Use light duty 173 & 174 end stops for small dinghies and low load applications Heavy duty 263 & 264 end stops can absorb the shock loads of unintentional jibes and are used on larger dinghies and small keelboats