Davis Round Sail Track Stop 
Round Sail Track Stops
Round 0.50" dia. x 0.875" (13 x 22mm)
When it's time to lower your sail you can rely on Davis' Round Sail Track Stop to hold your sail and its slides in place on the mast and boom. Large knurled wheels are released with ease. Made of heavy-duty, black anodized aluminum and marine garde nickel plated brass.
Quick Guide (pdf)