That's what I was thinking it was for, I've tried to us a flat head screw driver to turn the inside screw but won't turn. Any idea what type of tool is required to adjust the drag?I have that vise... I think it raises a bearing against the centre post, pulling the plates apart, and thus adjusting the drag on rotation... I think I’m right... but as such it’s sort of a two spead adjustment.
Thank you, that's just what I finally figured out.The outside part is a spanner nut, it is a form of lock that puts the set-screw in a bind to prevent it from moving on its own, you will need a spanner screwdriver (a screwdriver that is missing the center part of the blade) that fits the outside ring, once loosened it should allow the adjustment screw to be turned easily. Normally a locking spanner nut is only internally threaded and binds against the shoulder of the threaded hole and is loosened as any other bind nut in the same direction as the thread of the set-screw, but from what Papart said it seems to be double threaded which may mean how it's built it could need to be turned either right or left handed to loosen it and it is possible that turning it too much in the right direction could also re-set the lock in the other direction, you will have to go by feel and experimentation..