A think that "A" possibly is not lever (clef) and is not a part of this hangonne. May be it something on the body of the man. In this case details "B" and "C" may be just a one simple holder for a tinder which is fixed on a stock by nail. It looks like sistem of Giorgi Martini. I think that hangonner had to push on side "B" by thumb to turn it around the nail. In all case we don't know exactly
p/s
I have made mistake. It is not spanish tapestry but portuguese tapestry