As an Engineer I have all the coolest software you can possibly imagine to figure all this junk out (this is what I do for a living).
Just for my own information I just ran all the calculations thru my FEA software (it's like a 20k program lol) with interesting results.
According to the FEA simulation the Nylon bolt exceeds the yield strength of the nylon, at a little over 125 lbs of direct force ( my rough test with the fish scale verified that test). I was pulling on the AMA and damage to the bolt begins at around 60 lbs of force (because of the leverage (aprox 2x force)).
However I made a significant discovery while doing my tests that Tom Kirkman has been telling us all along (he is very clever). After the 75+ to 85 lb test I removed the shear bolt and put in a new one (did the same test twice just to make sure). The first sheer bolt (because it is threaded) showed deformation on the threads (the threads were crushed a little because we exceeded the 125 lbs of direct force on the sheer bolt (because of leverage, we are pulling on the AMA further out, but the sheer bolt is about halfway inboard (basically doubling the direct force on the shear bolt))). This is one of the unique things about plastics (they have very little memory). What this means is each time the AMA takes a 65lb or greater shock there is some damage and deformation to the sheer bolt. So in other words if you tug on the AMA 4-6 times with 65 lbs of force it may break eventually (via material fatigue and creep), I'm just guessing here but maybe a dozen hits at 50 lbs force, and it may break, and just guessing 30-40 or so 40lb hits and it may break. Basically the threaded shear bolts are ticking time bombs ( lol)
Tom was exactly correct in his observations and statements (he replaces his pins on a regular basis with new ones ( quite probably the root cause of your problem). Going to a pin without the threads would lessen the creep factor in the plastic, because it is a cut thread the plastic creeps each time it is hit with a smaller than ultimate (125 lb) blow. According to my FEA anything over about 85-90 lbs tugging force on the AMA can possibly take the pin out on the first try.
In other words if your AMA takes an 85 lb hit, even if it didn't break the first time, once it has begun deforming the next time it may only take 75 lbs to break it, (as per Tom's own observations).
I also measured the ball on the hull, according to the charts the bolt should be able to withstand 1400 lbs of sheer force, However because it is a thread, the factor of safety is exceeded at around 600 lbs direct side force. In other words that ball may be able to take a 500 lb hit, but that's not saying the brass insert won't be ripped from the hull. Because the force is amplified via leverage, I'm guessing about 200 lbs against the end of the AMA will snap that ball right off.
I'm just guessing off the top of my head here (based on experience with such things) but I would think it would take around 500 lbs of direct force to elbow the AKA bar material (just a guess on my part). Because of leverage and the mounting point to the brace, if you apply around 200 lbs force to the AMA if the ball doesn't break off, the AKA bar will likely fold and elbow.
Bottom line summary of my results:
The worst thing you can possibly do to your AMA's structural integrity is to put a stainless bolt into the brace replacing the Nylon sheer bolt. The reason for this is the direct force pushing back on the AMA is concentrated and amplified at that small point 1/2 way down the bar, the result is the AKA bar will elbow and fold with as little as 200 lbs force (this is just simple physics and leverage). If you want to prevent the AKA bar from elbowing, allow the nylon bolt to go ahead and sheer off. This allows the entire length of the AKA bar to obsorb and distribute the force and hinge on the hinges (can't possibly elbow). By adding a safety line lets say to the bow, then tied to the center of the AMA, all the forces are direct (no amplification or leverage), so if you have a 250 pound test line tied to the bow (I have 1/4" nylon 250 lbs test line tied from my bow to the center of the AMA), it will take 250 lbs of direct force against that AMA to break that line (if you hit something), but once the line is broken, the AMA and AKA bars just fold out of the way harmlessly (no damage to the AKA bars or the AMA's, or the ball (simply not possible)).
If you have a stainless bolt in the brace, either the ball will pop off (200 lbs force against the AMA), or the AKA bar will elbow (200 lbs force) more likely both, or the ball will be ripped from the hull. Personally I would much prefer to replace a small nylon bolt, and maybe a small piece of rope (all of which can be replaced on the water) than have to replace either my hull, or the AKA bar, or the brace ball, likely all three.
Now here is the reason for using the nylon stretchy line. When you hit something your boat is moving, right away the shear bolt breaks, The nylon rope completely obsorbs your forward motion energy as it stretches and bring the boat to a halt. You will never in a million years break that 250 lb test rope if the collision is being created by your forward motion, because just the act of stretching that rope stops your boat (like a big rubber band stretching). Once your forward motion is stopped, the stored energy in the rope pushes you boat backwards in the water ( like a giant shock obsorber). Resulting in no damage of any kind to your TI ever..... (besides have to replace a shear bolt once in a while). Hobies design is brilliant, the only thing they didn't count on is eventually boats being modded, and going faster, or being taken out into open ocean, and big waves. But by adding the simple safety line I have been trying get everyone to understand very frustratingly now for over 5 yrs now, that totally compliments Hobies original design and intent, the only additional thing the line does is if you do happen to break a shear bolt while out on the water, the lines only purpose is to prevent the AMA from folding in completely so you can make repairs and then get back underway.
My little line thingy totally compliments Hobies incredibly good design and collision damage prevention system that they so cleverly designed into every Island boat.
Hopefully everyone now gets it.