here is the stainless steel plate and mast receiver
here is the mast base fitting with socket insert
since the mast base insert is made of epoxy saturated end grain white oak, I didn't want to ever have to worry about a remote possibility of rot so where the screws attach the plate, I over drilled holes in the wood and filled the voids with epoxy and cabosil. after this cures, I will drill holes for the screws and fasten the base plate to the mast base structure. This way, any water that makes it's way past the fasteners will never be in contact with wood.
here's the finished bonded mast base. I bedded it in place with a thickened mixture of cabosil and epoxy. To insure a neat edge, I rubbed the seam with peel ply. When it cures, I'll rip the peel ply off and it should reveal a clean edge seam.