What do you use to attach the mainsail tack to the boom? Right now I have a rod that inserts through the eyelets on top of the boom. I just align the cringle(?) in the tack between the eyelets and thread the rod through all three holes. Problem is that the rod has a circlet at one end but the other end tapers and there is nothing to keep it from backing out.
You should have a sorta bent big pin with a tiny pin in the end to allow it to go through one of the sides on the boom but not the other (there's a small slot so the pin can pass through the one side). Discussion here: http://cpyoa.geekworkshosting.com/forum/index.php?topic=7352.msg54240#msg54240 (http://cpyoa.geekworkshosting.com/forum/index.php?topic=7352.msg54240#msg54240) but photo included: (https://www.dwyermast.com/images/DH359-1LX_linedrawing.gif)
The parts are available from Dwyer Mast (price list at the link above), and here's a different view (you need #9).
(https://www.dwyermast.com/images/dh3541lxy_linedrawing.gif)
Sound like yours went missing in the past and was replaced with a simple detent pin of some sort like this (with perhaps the ball missing):
(http://images.jamestowndistributors.com/woeimages/fasteners/250_250/sdg-193410.jpg)
which will work if you can ensure both sides are secured/prevented from passing through, but is probably not ideal. A long enough clevis pin may work, but for the minimal price difference you may want to get the original part.
(http://www.homedepot.com/catalog/productImages/1000/b1/b10943d3-a3be-4de4-8f49-876fa9cc630d_1000.jpg)
HTH,
Justin
Thank you. Perfect answer. You even nailed the detente pin as the substitute (the ball is intact but I didn't think it relevant).