The master-tools, here illustrated and described, comprise all that are necessary for plain machine-work in every description of metal; and if they are made of the precise shape, and according to the given instructions, they will perform the full amount of duty here allotted to them, which, though it may appear to be unusually great, may be thoroughly relied upon for metal of any ordinary degree of hardness. Nor can any less amount of duty be obtained from them without evidencing inferior mechanical skill either in making or using the tool. It is true economy to obtain from a cutting tool its utmost amount of duty, which, though it may entail a little more drawing out and grinding of the tool in a given time, does not involve any more as compared to the quantity of work performed. It is well within the mark to say that at least one third more duty, in a given time, may be obtained from cutting-tools for metals (used in all machines having variable speeds and feeds, such as the lathe and the shapingmaehine), than is obtained in the usual practice of our machineshops, especially in the larger ones.