Such measures are made of pieces of plate iron that are bent to a tubular form, to fit loosely on the bolt, pin, or rod to be measured. They are made also of thin iron pipe which is sawn into pieces of the required lengths. If necessary, two or three tube-measures may be used at one time on one bolt or pin, the measures being placed end to end, and extending along the bolt to the length desired.

Measures of this sort are used to indicate the commencements of keyways in the ends of bolts that require punching instead of drilling. After a measure of proper length is selected or made, it is put upon a bolt or pin while at a proper heat for punching; the portion of the bolt projecting beyond the measure is next put into the gap of a bottom tool, and the punch is held on the bolt-end and tight against the measure; while the punch is thus situated, it is driven half way through the work from both sides, the tube is next taken off, and the keyway finished with further punching and drifting.

These measures are useful also for indicating the intended junctions of bolt-screws with the adjoining portions of the bolts, when it is necessary to reduce the end for the screw to a diameter which is shorter than the diameter of the adjoining part. A tube-measure may be also used for a pin, bolt, or rod when screwing is not intended. For such purposes the tube is put upon the work, and the rounding tool, set hammer, fuller, or other tool to be used is put close to the measure, and the drawing down commenced while the set hammer is tight against the measure, so described for key-way punching.

Another use for such measures consists in applying one to a great number of bolts that require to be forged to one length ; in these cases the cutting-off chisel is put close to the end of a measure while it is on a bolt, and a correct length is thus ensured. A measure for this purpose on a bolt is represented by Fig. 223.

A usual mode of measuring lengths in bolts or other work without a tube, consists in marking the length with chalk upon a straight-edge of convenient length, to be held to the work by the hammerman ; and while he holds one end of the straight-edge tight against the shoulder of the bolt-head, the smith puts the reducing tool or chisel to the bolt and also opposite the chalk mark on the measure; while the smith thus holds the tool, the hammerman takes away the measure and drives in the tool with his hammer.

The mode of making tube-measures, and also other work of similar shape, consists in bending the pieces of plate while at a suitable heat. If several are to be made at one performance, all the pieces may be first cut and prepared previous to bending, and all may be cut small enough to form spaces between the extremities after being bent to a tubular form. Such a space is shown in the tube on the bolt shown by the Figure (223), and the advantage of such an opening consists in its allowing the plate to be bent in an easy manner. The length of the tube is the distance along the bolt to which the tube will extend when finished, and the piece of plate is cut a trifle longer to admit a little filing or adjusting to a proper length. After a sufficient number of pieces are prepared, they are curved while heated by driving a piece of round iron or steel on to the plates while lying across some convenient gap. For such bending, the gaps of half-round bottom tools are suitable, and after the round iron shaper is driven in to a proper distance, the curving of the tube is completed with a couple of top and bottom tools of a suitable size, while the round iron is in the hole and held by the workman as an ordinary nut mandril. After the tubes are made, the two bearing extremities of each one are adjusted to a precise length, and made parallel to each other; this is effected by placing the tube with one end upwards on an anvil and flattening with a flatter, and afterwards with filing, if necessary.