I missed this thread, or I would have replied sooner.
The original handrails are (were) teak, and secured through the cabin top with really long Phillips head screws.
I ordered replacements from McMaster-Carr.
The way that they are fastened is through the inner handrails, through the cabintop liner, through the deck, through a spacer, through the handrail, and into a nut that is set into the handrail with a teak plug epoxied over it. Thus;
I couldn't stand the teak looking like crap, so I replaced mine with 1" Stainless Steel box tube. The problem with that is the ends must be tapered from 1" to 1-7/8" (if I recall correctly).
I got it done and this is the result, and how they look today;