Chain stop, or cord stop. Clockmakers' term for a part that keeps the fusee from turning when the watch has been fully wound. See Horology, [plate X, Key AA,] Figure 44, showing a top view of the stop and its stud: ig is the end of the piece that blocks the fusee once the watch is wound all the way up; PI is a slender blade with a hole through it that joins the arm to the stud, as explained in the article Chain stop. This mounting allows the stop to pivot on its stud, so part g can be nearer or farther from the plate. Light spring r (Figure 44) keeps the stop a certain distance from the plate, so that the nose of the fusee can turn past it without touching. The stud is located so that the chain passes over part g , but when tip g touches the plate, it encounters the nose of the fusee as it is turned in the opposite direction to when the watch is going. Once this arrangement has been clearly understood, here is how the part keeps the fusee from turning once the watch is fully wound.

When a watch is being wound, the chain moves closer and closer to the upper plate or the balance, as is readily seen by winding a movement removed from its case. Now when the watch is almost fully wound, the chain is very close to the plate, but as we have said, it passes over the chain stop, which is held up by light spring r ; consequently, when it approaches the upper plate, the chain lowers the stop and brings it closer to the plate. This continues until tip g is resting against the plate and can go no lower; then the nose of the fusee encounters it and can no longer turn in this direction. This avoids the risk of breaking the chain, as would almost inevitably happen if the watch were wound beyond a certain number of turns. See Fusee, Fusee hook, Chain, Chain stop, etc.