The fluting of a hob consists in forming narrow grooves along the entire length of the screw. Each groove has a curved bottom and two straight sides that are slightly inclined to each other, in order to make the mouth of each flute wider than its bottom. The lengths of all the flutes are parallel to the entire length of the hob ; consequently, the depth of a flute is the same at one end as at the other end, because the hob-screw is parallel. Both sides of a hob-flute are sharpened to provide two rows of cutting teeth ; the hob will therefore cut whether the stemend of the screw is first entered into a nut, or whether the opposite end, named the plug end, is first entered. A hob is never required to cut out more than a very thin scraping from a nut or other piece of work, so that very little room for shavings is provided in the flutes - a large amount of bearing surface being allowed because friction is of no consequence.

The fluting of a long taper tap consists in making long narrow grooves having curved bottoms along the entire length of the screw. In almost every tap which is made, whether long or short, the number of flutes is either three or five, the proper number being three, because with three flutes the friction surface of the tap-screw while in use is at a minimum. The object when making a tap-flute is to provide a row of cutting teeth along the entire length of the screw, and to make a space for containing the shavings cut off while the tap is in use. The large quantity of shavings made with a tap renders it necessary to make wide grooves, and the bearing surface is at the same time reduced to avoid friction. Each flute of a tap forms one row of cutting teeth, the cutting edges of which are in a plane extending through the tap's centre and along its length; and through the tap having three flutes it is said to have only three cutting edges, although it has two or three hundred. While the implement is in use all these edges are successively made to cut, each tooth cutting off only a small quantity as the tap is rotated, and gradually forced through the nut, or other work being tapped. Through the tap-screw being taper» the screw which is being formed in the nut is gradually and continually enlarged, until the thickest portion of the screw has entirely passed through the hole. If the tap-thread at the seventh mark is completely formed, slightly tapered, and polished, as directed, the nut-screw will be fully formed and nicely polished. A long taper tap, whose screw is well shaped and hardened, and the flutes properly formed, will screw several thousands of nuts, so that every hole shall be of precisely the same diameter, and every nut will fit a screw-gauge plug in the same manner. Although, during the tapping of ten thousand nuts, the point of the tap becomes blunt several times, and requires frequent grinding, which may make it an eighth of an inch thinner than its original thickness, the parallel portion is of the same thickness as when newly hardened years before, because this portion is introduced to the holes in such a gradual manner by means of the taper part adjoining.