[Illustration: Fig. 6. Large Double-jointed Calipers] Kinks in Inside Calipering Close measurements may be made by filing two notches in each leg of an inside caliper so as to leave a rounded projection between, as shown at _E_, Fig. 7. Then, with an outside caliper, _D_, the setting of the inside caliper, _B_, is taken from the rounded points. The inside caliper can be reset very accurately after removal by this method. A still better way is to have two short pins, _CC'_ set in the sides of the inside caliper legs, but this is not readily done as a makeshift. To measure the inside diameter of a bore having a shoulder like the piece _H_, the inside caliper _F_ may also be set as usual and then a line marked with a sharp scriber on one leg, by drawing it along the side _G_. Then the legs are closed to remove the caliper, and are reset to the scribed line. Of course, this method is not as accurate as the previous one, and can be used only for approximate measurements. [Illustration: Fig. 7. Methods of Inside Calipering] To get the thickness of a wall beyond a shoulder, as at _K_, Fig. 7, set the caliper so that the legs will pass over the shoulder freely, and with a scale measure the distance between the outside leg and the outside of the piece. Then remove the caliper and measure the distance between the caliper points. The difference between these two distances will be the thickness _M_. Inside Calipers for Close Spaces In Fig. 8 are shown a pair of inside calipers which are bent so as to be well adapted for calipering distances difficult of access, such as the keyway in a shaft and hub which does not extend beyond the hub, as indicated. With the ordinary inside calipers, having straight legs, and which are commonly used for inside work, it is generally impossible to get the exact size, as the end which is held in the hand comes in contact with the shaft before both points come into the same vertical plane. The engraving plainly shows how calipers for this purpose are made, and how used. Any mechanic can easily bend a common pair to about the shape shown to accommodate this class of work.[3] [Illustration: Fig. 8. Inside Calipers for Close Spaces] Surface Gage with Two Pointers Figs. 9 and 10 show a special surface gage, and illustrate an original idea which has been found to be a great saver of time and of milling cutters. It can also be used on the planer or shaper. By its use the operator can raise the milling machine table to the right height without testing the cut two or three times, and eliminate the danger of taking a cut that is liable to break the cutter. This tool is especially valuable on castings, as raising the table and allowing the cutter to revolve in the gritty surface while finding the lowest spot is very disastrous to the cutting edges. [Illustration: 10]