Dimensions of Whitworth Screws.
| Diameter of screw | Number of threads per inch | Diameter at bottom of thread | Diameter of screw | Number of threads per inch | Diameter at bottom of thread | Diameter of screw | Number of threads per inch | Diameter at bottom of thread |
|---|---|---|---|---|---|---|---|---|
| 1⁄8 | 40 | ·093 | 1¼ | 7 | 1·067 | 3½ | 3¼ | 3·106 |
| 3⁄16 | 24 | ·134 | 13⁄8 | 6 | 1·162 | 3¾ | 3 | 3·323 |
| 1⁄4 | 20 | ·186 | 1½ | 6 | 1·286 | 4 | 3 | 3·573 |
| 5⁄16 | 18 | ·241 | 15⁄8 | 5 | 1·369 | 4¼ | 27⁄8 | 3·805 |
| 3⁄8 | 16 | ·295 | 1¾ | 5 | 1·494 | 4½ | 27⁄8 | 4·055 |
| 7⁄16 | 14 | ·346 | 17⁄8 | 4½ | 1·590 | 4¾ | 2¾ | 4·284 |
| 1⁄2 | 12 | ·393 | 2 | 4½ | 1·715 | 5 | 2¾ | 4·534 |
| 5⁄8 | 11 | ·508 | 2¼ | 4 | 1·930 | 5¼ | 25⁄8 | 4·762 |
| 3⁄4 | 10 | ·622 | 2½ | 4 | 2·180 | 5½ | 25⁄8 | 5·012 |
| 7⁄8 | 9 | ·733 | 2¾ | 3½ | 2·384 | 5¾ | 2½ | 5·238 |
| 1 | 8 | ·840 | 3 | 3½ | 2·634 | 6 | 2½ | 5·488 |
| 11⁄8 | 7 | ·942 | 3¼ | 3¼ | 2·856 | |||
Gas Threads[1] (Whitworth Standard).
| Diameter of Screw | 1⁄8 | 1⁄4 | 3⁄8 | 1⁄2 | 5⁄8 | 3⁄4 | 1 | 1¼ | 1½ | 1¾ | 2 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Number of threads per inch | 28 | 19 | 19 | 14 | 14 | 14 | 11 | 11 | 11 | 11 | 11 |
[1] Used for wrought-iron and brass tubes.
Representation of Screws.—The correct method of representing screw threads involves considerable trouble, and is seldom adopted by engineers for working drawings. For an explanation of the method see the author's Text-book on Practical Solid Geometry, Part II., problem 134. A method very often adopted on working drawings is shown in fig. 15; here the thin lines represent the points, and the thick lines the roots of the threads. At fig. 16 is shown a more complete method. The simplest method is illustrated by figs. 10, 11, 13, and 14.
Here dotted lines are drawn parallel to the axis of the screw as far as it extends, and at a distance from one another equal to the diameter of the screw at the bottom of the thread.
| Fig. 10. | Fig. 11. |
Forms of Nuts.—The most common form of nut is the hexagonal shown in figs. 10, 13, 14, 15, and 16; next to this comes the square nut shown in fig. 11. The method of drawing these nuts will be understood by reference to the figures; the small circles indicate the centres, and the inclined lines passing through them the radii of the curves which represent the chamfered or bevelled edge of the nut. In all the figures but the first the chamfer is just sufficient to touch the middle points of the sides, and in these cases the drawing of the nut is simpler.