The tool shown in Fig. 51 is used for gaging taper threaded holes in boilers when fitting studs. It is a simple, though very useful and economical tool, and it will doubtless be appreciated by those having much work of this kind to do. The hole in which the stud is to be fitted is calipered by filling the threads of the plug with chalk, and then screwing the plug in the hole. When the plug is removed the chalk will show exactly the largest diameter of the hole.[29] Contour Gage [Illustration: Fig. 52. Setting Contour Gage to Turned Sample] [Illustration: Fig. 53. End View of Contour Gage] Figs. 52, 53 and 54 illustrate a special tool which will be found of great value in certain classes of work. The need of some such device becomes apparent when patterns and core boxes are required to be accurately checked with the drawings of brass specialties, in particular. The tool is applied to the work, and the wires pressed down onto the contour by using the side of a lead pencil. Of course, patterns parted on the center could have their halves laid directly on the drawing without using the contour gage, but some patterns are cored and inseparable. Such a tool proves a relentless check upon the patternmaker, who, by making the patterns larger than necessary, can cause a considerable loss in a business where thousands of casts are made yearly from the same patterns. As a ready and universal templet it is very useful.[30] [Illustration: Fig. 54. Testing Core-box with Gage] Testing a Lead-screw [Illustration: Fig. 55. Micrometer for Testing Lathe Lead-screw]