The gauges employed for turning paddle-shafts to the exact required diameters and lengths are the same as those for straight middle-shafts, and others of similar forms. The gauges for indicating the several lengths are termed length-gauges, and include bar gauges with short pointed arms, wood gauges consisting of straight staves of wood, radius gauges having adjustable scribers, straight wire gauges, sheet iron gauges, and inside callipers. For measuring diameters, outside callipers and wire gauges are used, and in a few cases, but very seldom, gap-gauges made of sheet iron are used. Sheet gauges are not generally available for measuring large diameters, because of being too large and occupying so much room.

A gauge to show the several lengths and distances between the shoulders of a paddle-shaft can be made at any time, and the axle, or a pair of them, can be completely turned with regard to the gauge, or gauges, because the outer pillow-blocks, which are to be situate in the paddle-boxes, can be accurately fixed in the exact places to suit the outer bearings of the axles; and this fixing can be done after the axle is entirely finished and in its place. But a gauge to show the lengths belonging to a middle-shaft cannot be properly made until its two entablatures are finally adjusted and fixed. The gauge should be made or marked while the ship is afloat, which is to be the ordinary condition when the axle is in its place. The material used for the gauge is a thin bar of iron, or of dry wood, wood being suitable because of its lightness, if it is to be immediately used, and is therefore not liable to alter its length while in use. When the gauge is being scribed, it is held edgeways in contact with the brasses; consequently, it is to be held in the same position when on the axle which is to be turned thereto, to avoid being misled by the bending of the gauge, which would result if not placed edgeways. The marks on the gauge should indicate the exact distances of all the shoulders of the brasses from each other, allowing for any irregularity in any brass, if any exists; and whatever room may be intended for the shaft can be afterwards allowed when the shaft has been marked by the gauge.

In order to cause all the four shoulders of the two shaft-bearings to be exactly in their proper places, to suit the four shoulders or sides of the brasses, and to cause both bearings to be of a correct length for their respective brasses, the turner must attend to two things. These are, the total lengths between the shoulders, as indicated on the gauge, and the length of each brass individually considered with regard to its respective bearing. To proceed orderly, he first smoothly turns all the four shoulders of the two necks to the proper length from each other, as shown with reference to the gauge. When this is done, each neck should be next fitted to its respective brass; and at this fitting both shoulders of each neck must be equally reduced, to give the requisite amount of room for the brass, which is about a thirtieth of an inch for a large brass. By adopting this plan the length between the two outer shoulders of the shaft, when finished, will be about a sixteenth greater than that indicated on the gauge, and the length between the two inner shoulders will be about a sixteenth shorter; consequently, the needful amount of room required for the shaft in its brasses is secured, and is also equally distributed to the shoulders of both bearings. The smoothing of these shoulders is accurately done at the first, previous to finishing the mid-parts of the bearings, and is so done as not to require anything whatever to be afterwards removed when the curved corners and cylindrical parts are being finished.

The completion of the necks now proceeds with respect to the brasses only, the lengths having been finally determined; consequently, it is now only necessary to turn the curved junctions and the straight mid-portions of the bearings to the proper diameters, by means of pointed corner tools, or with springy tools, according to the amount to be removed.

The final reduction of a bearing neck should be effected with reference to one of the half-brasses belonging to it, the brass being suspended over the neck, and lowered into its place, when a trial is to be given. After being lowered to the shaft, the brass will easily be moved to and fro, if the neck is small enough; but if not, the brass will stick tight, and therefore needs further reducing in some part. It is necessary to put some tange upon the surface, previous to trial, in order to plainly show whether the cylindrical parts are in contact, or whether the curved junctions only are in contact; by which means the risk of reducing the neck at a place where it is not necessary is avoided. At this fitting of the brasses nothing whatever is to be removed from the four shoulders ; these are already correct, as before stated, both for the lengths of the brasses individually and for their distances apart when in the headstocks.

The length-gauges now remaining to be mentioned are straight wire-gauges, bar-gauges, radius-gauges, and inside callipers. A straight wire-gauge is useful when only one bearing-neck is to be fitted to a pair of brasses without special regard to its distance from any other neck or shoulder. In this case the wire is filed until its two extremities are as far apart as the length of the brasses. This distance is obtained either by accurately measuring the length of the brasses with an outside calliper, and filing the points of the gauge until they fit the calliper, or by placing a straight-edge to each end of the brasses, and adjusting the gauge to the distance between the straight-edges. When the gauge is in use it is placed in between the two shoulders of the neck, and the neck is lengthened until it is as much longer than the wire as the intended amount of looseness for the brass when in its place.

A pointed bar-gauge, or a radius-gauge, is only useful for measuring a shaft when stated distances are to be marked between the centres of any two bearings, or between any two shoulders, or when the centre of a shaft's length is to be found, and all other lengths measured from the centre. An inside calliper is used for lengths when a shaft-end for a lever is being finished to its exact length to prevent it extending beyond the face of the lever-boss when connected. In this case an outside calliper is first adjusted to the length or distance of the hole through the boss, and an inside calliper is adjusted to the outside one.

The wire gauges mentioned for measuring diameters are highly useful and accurate in their indications. These should always be used for large objects because they do not alter while in use, and mislead the operator. Whereas, if large callipers are used for measuring large objects there is always a risk of the legs shifting and indicating wrong dimensions. For the measuring of a hole not exceeding three or five inches in diameter, an inside calliper can be carefully adjusted so that its points only very gently touch the surface of the hole, and the correct diameter can thus be shown. But if a large calliper is adjusted to a hole of twelve or fifteen inches in diameter, the legs will be slightly bent, either inwards or outwards, in the course of using them, but without their being at all shifted with regard to their joint-pin ; consequently, the distance between the calliper-points is either too little or two much, the exact distance depending on the position in which the calliper is held or placed.

In order to correctly turn a bearing neck to a suitable diameter for a pair of brasses, the diameter of the hole in the brasses must be correctly measured while both brasses are together in their positions in which they were bored. Either an inside calliper or a wire gauge is then adjusted so that its points gently touch the two sides of the hole, and it is requisite to measure several parts of the hole, to find the smallest place. When the gauge is fitted and is to be used, it should be laid with its length horizontal, and upon a piece of flat board, or plate, or, as a substitute, on the floor at the turner's feet. An outside calliper is now adjusted until its points gently touch the points of the wire, being careful to hold the calliper during measurement, so that it stands vertical on the plate or floor. By reason of this being the proper position of the calliper during adjustment, it is also necessary to hold the outside calliper in the same position when it is applied to measure the bearing-neck in the lathe.

It is to be noticed that no bearing-neck can possibly rotate in a couple of brasses if their hole is no larger than the neck within, unless sufficient power should be applied to tear out some of the metal at the time of rotation. By not considering this fact, and by attempting to make what are termed good fits, a great number of misfits are made; and much time is occupied in subsequent fitting. The difference between the diameter of a neck and the diameter of its brasses, when both are properly adapted to each other, is much greater than usually supposed. For a neck about six inches in diameter, it is about a sixtieth or a fiftieth of an inch, and for one of fifteen or sixteen inches, at least a thirtieth of an inch.