In fitting a new roller and pin in a lever watch, first procure a sott rough roller and broach out the centre hole to go on the balance-staff to the correct height. Place it on an arbor and in the turns or watch lathe, turn the pipe to the right diameter and length, turn both sides of the roller flat, and reduce its diameter until, when on the balance-staff and in the watch, the lever has just a little shake at each side when the guard pin rests against the roller edge. Then measure the position of the ruby pin-hole so that its pin will come well in the lever notch. Drill it with a small drill and broach it out until a pin fitted in it just enters the lever notch freely. Then file the passing hollow for the guard pin to pass at each beat. Try the action in the watch, and, if correct, harden the roller and temper to a red colour. Polish the roller on the face, and especially on the edge, with crocus and oil on a steel polisher.