There is little point to putting sealant in the fastener hole in the fitting itself. The area where the sealant is required is between the fitting and the deck, and that is why you're supposed to countersink the top of the fastener hole... since that is where the seal that prevents water from getting into the boat really is.
Also, I would point out that the two-step procedure for allowing the sealant to cure has been debunked. It is very difficult to tighten the fasteners properly without breaking the sealant adhesion them. It is also completely unnecessary if the holes have been countersunk so that the sealant can form a natural "o-ring".
I'd also point out that on high load fittings, like cleats, the two stage cure and tighten process can leave the hardware less than completely tight, since the sealant will resist tightening the bolts as snugly as they should be and lead to premature sealant failure as well as possibly a weaker installation overall--since friction between the deck hardware and the deck caused by fully tightening the through bolts are a considerable factor in the strength of the mounted hardware.
Originally Posted by Uglydave
What about a countersunk screw in a counter sunk hole? I recently installed midship cleats, I over drilled and filled the holes with epoxy then laid in Sicaflex 291 before pulling the cleats down to 1mm from the deck using spacers (I put Sicaflex inside the countersunk recesses) after allowing the sealant to cure, removed the spacers and nipped up the nuts.
Should the countersunk recess and the head of the countersunk bolt have a different angle of countersinkedness (is that a word?) to allow some amount of sealant to remain under the bolthead?
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