Ceased bolt in windlass #solution

Daniel Alexander Thompson

Team Amel

Photo attached. 

The head of a 6x20mm bolt has been severed and the threading is ceased into the cast of the windlass. I've attempted to turn it with pliers and a plumbers wrench. I've tried WD40. No movement at all. 

I don't know the name of the part that the bolts secure.

Any suggestions for how to get the bolt out or a temporary fix to stop the chain wrapping under the gypsy. 

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