It's definitely a bolt and it goes right through the teak and through the glass too.  I haven't actually seen the nut, just assumed it was there because the other bolt came out without trouble; I guess the nut was held in place somehow.  Today I just got frustrated and since there was enough of the neck of the remaining bolt showing I cut it off with a hacksaw.  I removed the rail without further problem though there was a hidden screw under the chock to watch out for.  The remaining part of the bolt did not push through the glass though...mysterious.  I'm going to shove my digital camera up there and see what's going on.  I'm concerned that the chock on the other rail may not show enough of the bolts for me to cut.

The teak is very hold and has not been re-done for at least 10 years.  I'm being tempted by slotted toe rails sad

I'm removing the teak toe rails which are screwed in.  At the stern there are two chocks, one on each side, for dock lines.  These sit on top of the toe rail and are bolted rather than screwed through the toe rail.  Even though I am a reasonably good contortionist, try as I might I cannot reach or even see the nuts for the chocks as the are tucked under the uplift of fibreglass that rail sits on.  Any suggestions?

I have the fine spidery cracks in some of the gelcoat around stanchions and a couple of other places on the deck.  This is called "checking" if it's on a guitar's finish, I don't know if it has a name on boats. 

I want to do two things: 1) fill the cracks becuase I'm worried about water and freeze/thaw cycles  2) make it the same colour as the existing gelcoat.  Any recommendations?