Hi
@jssailem ,
The inserts I linked to are designed to be molded into an injection molded part. The don't expand. The whole point of the design is to maximumize load transfer surface area from the very strong stainless steel insert to the far less strong plastic it's molded into. You don't press them in, you place them in the mold and then mold around them.
I should say that I have not used these in fiberglass epoxy, I have only specified them for use in injection molded parts. If they were going to be subject to high pull-out loads, then I'd be less sanguine about them. But for a mast foot I think they'd work well--certainly better than what was in there!
I know that there are fasteners specifically designed to be molded into composites, such as those used on carbon fiber airframes or carbon fiber racing car chassis. But I don't know where to get them and, based on what I've seen, I think they would be difficult to retrofit in the situation
@JAC1 is dealing with.