hold up the mast? I assume you mean to pin the forestay to the bridal chainplate - you can use a spring loaded quick pin - i have never seen one break or fail and they make them in any size you could need on a beach cat
be careful not to leave it pinned (to anything) during storage as they have a history of becoming frozen/seized after a prolonged storage.
I have seen many people trying to get a pin out (with hammers, blaster rust remover, hacksaw) on the beach because it has frozen and preventing them from rigging.
Also i suggest you never use a quick pin on a brass clew plate or any brass / softer metal. I had one pinning my TheMightyHobie18 boom to the sail clew plate and it wormed its way out of the clew plate (at the worst possible place and time - as i was in a storm trying to tack away from a drawbridge)
they also make ringdings that are supposed to be easier to put on. I don't care for them as they are not easier to remove, and they get bent out of shape much easier than the standard ring
PS I would avoid Attwood products - they are the cheapest possible construction and materials ... go for a high quality part if it's supporting a critical part
I am looking for a clevis pin that is quicker than a standard with a ringding. I have seen the Attwood spring loaded with tether that looks like it would be perfect for what I want, but it is really just made for a cheap bimini. I cannot see what the problem would be. It is stainless (no idea what type) and 1/4 inch. But I would rather find something like it that is made to hold up something like the mast on a 16. I have been looking around and have had little luck. The quick pull type are hollow and I do not trust them. Would anyone trust the cotterless? I have not seen one with a tether, but I could easily fabricate one. I liked the Attwood because it looks like it has a nice lock in place mechanism. I am nervous about trying something like that on my shroud.