QUESTION 344. _How thick must a nut be, measuring lengthwise of the bolt, so that the thread in the nut will be of equal strength to that of the bolt?_ _Answer._ Its thickness must be equal to the outside diameter of the screw. TABLE GIVING PROPORTIONS OF THE UNITED STATES OR SELLERS STANDARD SYSTEM OF SCREW-THREADS. =========+=========+============+============= | |Diameter of | | |screw at the|Width of top Outside | |root of the |and bottom of diameter|Number of| thread in | thread in of screw| threads |decimals of |decimals of in inches| per inch| an inch | an inch ---------+---------+------------+------------- ¹⁄₄ | 20 | .185 | .0062 ⁵⁄₁₆ | 18 | .240 | .0074 ³⁄₈ | 16 | .294 | .0078 ⁷⁄₁₆ | 14 | .344 | .0089 ¹⁄₂ | 13 | .400 | .0096 ⁹⁄₁₆ | 12 | .454 | .0104 ⁵⁄₈ | 11 | .507 | .0113 ³⁄₄ | 10 | .620 | .0125 ⁷⁄₈ | 9 | .731 | .0138 1 | 8 | .837 | .0156 1¹⁄₈ | 7 | .940 | .0178 1¹⁄₄ | 7 | 1.065 | .0178 1³⁄₈ | 6 | 1.160 | .0208 1¹⁄₂ | 6 | 1.284 | .0208 1⁵⁄₈ | 5¹⁄₂ | 1.389 | .0227 1³⁄₄ | 5 | 1.491 | .0250 1⁷⁄₈ | 5 | 1.616 | .0250 2 | 4¹⁄₂ | 1.712 | .0277 =========+=========+============+============= PART XVII. TENDERS. QUESTION 345. _What are locomotive tenders for?_ _Answer._ They carry a supply of fuel and water for locomotives while they are running. QUESTION 346. _How are they usually constructed?_ _Answer._ Their construction is represented in figs. 204, 205 and 206. Fig. 204 is a side view, fig. 205 a longitudinal section, and fig. 206 a plan of an ordinary tender, which consists of a frame, _A A A A_, made of wood or iron,[82] mounted on a pair of trucks, _T_, _T_. The top of the frame is covered with planks, _B_, _B_, which form the floor of the tender. On top of this floor a sheet-iron tank, _C C C_, is placed, which carries the supply of water. This tank is made somewhat in the form of a letter ~⊃~, as shown in the plan. It is made in this way so that the space between the two branches, _C_, _C_, or “legs,” as they are called, will give room for fuel. Around the upper edge of the tank a sheet-iron rim, _D D_, is riveted, so as to prevent the fuel from falling off when it is filled up above the top of the tank. [82] The frame represented in the engraving is made of wood. In the plan it is shown by dotted lines. QUESTION 347. _How is the tank filled with water?_