Originally Posted by billr
Just one thing to not forget (though its probably obvious to this group) is that a quarter inch bolt which is not threaded by the head
will have a greater
shear strength than a quarter inch threaded rod.
In actuallity a 1/4" all-thread will stretch and stretch and will become loose after enough work against the rail. Then one will tighten and tighten and tighten and then eventually break. The root diameter of a 1/4" thread is 3/16". So, in effect it would be like using #10 bolts. If one is comfortable with that, then so be it!
Just to add to the problems, if it's not totally sealed off from the salt water
(Oxygen depletion) working it's way down the threads, then it will also fail just over time.