[Iscool]

Something that has worked for me in the past is to put a long closed-end (six-sided is better than 12) wrench (not socket) on it, and smack the free end of the wrench a few times with a hammer (poor man’s impact wrench).

I like to put a pipe over the end of the 6-point wrench, put steady pressure on it and beat on the end of the bolt (with the wrench stillon it) at the same time...Usually works...Sometimes have to attempt to tighten the bolt using the same process just until you feel it move and then work in the opposite direction...And I agree a wrench is better than a socket since there's less chance of the wrench slipping off and rounding the corners on the bolt...

[IYAS9YAS]

Sometimes have to attempt to tighten the bolt using the same process just until you feel it move and then work in the opposite direction

Yeah, I forgot about that. I've done that, too, trying to tighten, then loosen. Sometimes it's just enough to get it to work.

I've never tried the prying and banging on the head of the bolt. Usually, I've either had the bolt loosen, or I've had the head snap clean off, which, in turn, leads to me being admonished by any nearby sailors.

[Paul R.]

Noted. Maybe I can turn up a decent 6 point metric wrench set for not too much money: Need 17 mm for this. Funds are tight, but, I hate to buy a single...