While I don't totally picture what you are describing I suspect that the
bolt it to release the chuck from the tapered spindle. Comes the question
however.... Why would you want to remove the chuck? There is not much you
can do with the tapered spindle except put another chuck on it. But if you
must.... Before re-installing the chuck wipe the spindle and the tapered
hole in the chuck clean and coat both surfaces with oil to prevent rust
ceasing the chuck onto the spindle. Then with the jaws of the chuck
retracted into the chuck hold the chuck in place on the spindle and give it
a stout "bam" with the mallet. If the spindle and tapered chuck hole are
clean they will hold the chuck in place.
Don Dando