We just replaced this 5/8" shackle that was connecting our bob-stay to the boat, right at the waterline. That pin was responsible for supporting such useful items as: the mast. I can't believe how corroded it turned out to be, it's pretty much hollow inside. There was very little indication of a problem from the outside - when swimming this summer we noticed a little pitting, so put it on the to-do list. Makes you really think about checking your rig.