The final adjustment of the hole in a ring, whether soft or hard, must be effected by grinding. When a ring is to be ground with the same lathe in which it was bored, the ring is allowed to remain in the same condition fixed to the chuck, and the grinding-tool is fixed to the slide-rest in the same manner as a boring-tool. The grinder for rings is a long slide-rest tool having a lead or wood boss attached to one end, this end being put into contact with the surface to be ground while the other end is tightly fastened in the slide-rest tool-holders. The grinder is quickly moved to and fro in the hole by means of the lathe-traverse, and is made to bear either tight against the work or gently, by working the slide-rest screw. While moving to and fro, a mixture of emery and oil is applied to the grinder, and only the smaller sizes of emery are used. For each size of emery a separate grinder is required, which is one means of preventing irregular scratches in the work. The smallest emery, termed flour emery, is not necessary for adjusting to the required dimensions, but merely for a final polishing; the larger sizes of emery are therefore useful to quickly adjust the work, and the flour emery to smoothe it.

While adjusting a ring to its finished dimensions a standard gauge is necessary, and this is not the plug which is to be used with the ring, but another of the same diameter, and to this plug all the rings of one size are ground. By such means a number of rings may be made of one diameter, and all will be of the required diameter if the standard is right; but when each ring is made to fit merely its own plug, all are of different diameters, and all may be either too large or too small. The standard plugs used for such measuring should be hard, to avoid much of the tendency to wear, although steel ones that are not hardened may be employed and used for several years, if in the hands of proper workmen.