It is common for me to see people using quick pins on their standing rigging (rigging that holds up your mast). This is a really bad idea as these quick pins have a mechanical mechanism inside that can fail. Basically the pin typically has a ball-bearing type end that pushes out, which keeps the pin from sliding out of the hole it was inserted into (pic #1). If one pushes the button on one end of the pin it release the mechanism so one can remove the pin from whatever its inserted into. Other pins sometimes have a T-shaped mechanism on the end of the pin (called a drop cam and external spring... see pic # 2), but most use a ball-bearing type design as display in pic # 1).
So on many occasions I have seen this mechanism fail, resulting in the guts/pieces on the inside of the pin falling out, leaving a pin with no prevention from it pulling or wiggle out. And what is the result? Typically the mast comes falling down, particularly on sailboats with only a few wires holding up the mast.
Each year I warn people about this and most remove these pins and replace them with pins that have no such mechanism, just a pin with a wire ring on the end, or cotter pin (called a clevis pin, #3). Others do not and come back to me not only to get a new pin but many times a new mast, etc. which of course is a lot more costly than a simple pin replacement.
I might add not heeding this warning can also result in people getting hurt. Luckily in my 30 plus years in giving this warning no one has been hurt badly, just a few scraps and bruises, mainly because most take the advise and do the change.
Now quick pins can be used to attach running rigging, such as blocks, etc. to the deck, cabin top that run the sails. However using a quick pin on anything that functions with the boom, can be an issue, because if the block or some mechanism comes loose from the boom as a result of the quick pin failure there is some potential for damage and physical harm, particularly when one is in the act of jibing and the boom comes flying around.
So here are 2 pics showing how one should and should not attach a furling drum to the bow fitting with a quick pin. This lesson can apply when attaching any wire to a deck fitting. I am not showing in this pics attaching it to the deck fitting.
In the first pic shows a shackle (see pic #4 for an example of a shackle) with quick pin and lanyard, with the pin going through the furling drums permanently attached shackle (A). In the second picture I have edited out the shackle/quick pin combo to show how this system should be set up with a simple pin with wire ring or one can use a cotter pin if one is leaving the mast up (not trailering the boat). So the non-quick pin just goes through the furling drums permanently attached shackle (B).
I hope this article was helpful. If you have any questions or experiences about this please leave a comment.