The lathe-turning of the rings and plugs is effected by several methods, the mode selected depending on the quantity in progress and their dimensions. Plugs that are about a quarter or half an inch in thickness are turned of steel wire, without any forging being necessary. For such plugs the wire is cut into lengths, and their extremities are flattened to admit the centring process; this is effected by the aid of a couple of vee-blocks and a scriber-block, which are used on a table, as shown by Fig. 383. When the intended plugs are centred and drilled, they are separately turned with a small lathe and slide-rest in which is a vee-point tool. All the plugs are thus roughly turned to nearly their finished diameters, and are next smoothed to their proper dimensions with a springy tool and soapsuds. These diameters are not the finished diameters, but are larger, each plug being turned to fit a special gauge-hole, which is of a suitable diameter to allow a proper quantity of filing and grinding the plug to finish it.

Plugs about an inch or two inches in thickness, that are to be finally hardened, are also hardened at the commencement of the turning, after about a sixteenth of an inch has been turned off the entire surfaces of the plugs. After this hardening, they are again softened by gradual cooling, and next turned to their proper diameters for grinding. To turn a large number of plugs expeditiously, they are roughed in one lathe, smoothed with a springy tool in another lathe, and ground to the finished thickness in a third lathe. Cutter-rings also are useful to roughly adjust a number of plugs to one diameter. A cutter-ring or cutter-socket is a piece of steel which resembles an ordinary six-sided nut, having a number of cutting edges formed in the boundary of the hole. This hole is rather taper, and the cutting teeth are made by rifling, which consists in making coarse-thread grooves into the boundary of the hole while the ring is fixed to a chuck of a screw-cutting lathe. After the teeth are sharpened and hardened, the tool is used by slowly forcing it on to a plug or other piece of work which has been turned to allow only a small quantity for the ring to cut off. The cutting is effected by rotating the work in a lathe, and slowly advancing the ring along without allowing it to rotate; consequently it is held with a spanner, or some other kind of frame which may be fixed to, and made to traverse along with, the lathe-carriage. A cutter-ring of this class resembling a nut, is denoted by Fig. 516.

Plugs and other short pieces of work of similar character may be conveniently turned with a double lathe, similar to that represented by Fig. 528. Such a machine resembles two lathes having short beds which are together in one casting. On the bed are two mandril frames and two poppet-heads, each lathe-spindle being actuated by a driving band and starting apparatus which is distinct from that belonging to the other spindle. Each half of the machine has also its slide-rest and traverse gear, so that one can be worked quicker or slower than or without the other. When a piece of work of great length is to be turned, the two middle heads are taken from the bed, and the two traverse gears made to serve as one; by this means the entire length of the bed is always in use, and the affair is therefore economical for a great quantity of small work when only a few lathes are accessible.

Plugs whose diameters are three or four inches require holes to lighten the tools without impairing their efficiency. These holes are bored to about the lengths of the cylindrical parts, and the boring is partly done at the commencement, after the outer surface is roughly turned. The boring or drilling is effected either with a coned plate on a lathe or with a drilling-machine. All the large plugs are easily bored roughly in a vertical driller, and, after being bored by some means, the hardening is the next process to the first boring. When hardened, the plug is next softened, and again bored smoothly, and this time to the finished dimensions. The diameter of this hole is about half the plug's diameter, and is useful for turning the outside of the plug, which is done either by driving a spindle tight into the hole and fixing a gripper to the plug, or by allowing the edge of the hole to rotate on a large conical pivot.