These gates make it possible for the sail slides to drop to the boom.  Normally a bolt is used as a stop just above the gate to prevent the sail slides from falling out.   I had a problem getting the reefing tack low enough to suit me and the sail stacked quite high when lowered.  I made these out of Aluminum plate and bent them to fit (hammer and vice.). Picture on left is after 4 years of use, thought process is on right. They  work great and are a big improvement.