[Illustration: Fig. 191. Two-Foot Rule. Two Fold.]
[Illustration: Fig. 192. Steel Bench-Rule.]
[Illustration: Fig. 193. Back of Steel Square, Brace Measure.]
The _steel square_, Figs. 193, 194, 196, 197, is useful, not only as a straight-edge and try-square, but also for a number of graduations and tables which are stamped on it. There are various forms, but the one in most common use consists of a blade or "body" 24"×2" and a "tongue," 16"×1-1/2", at right angles to each other. Sargent's trade number for this form is 100. It includes graduations in hundredths, thirty-seconds, sixteenths, twelfths, tenths, and eighths of an inch, also a brace-measure, an eight-square measure, and the Essex board-measure. Another style, instead of an Essex board-measure, and the hundredths graduation has a rafter-table. The side upon which the name of the maker is stamped, is called the "face," and the reverse side the "back."
The brace-measure is to be found along the center of the back of the tongue, Fig. 193. It is used thus: the two equal numbers set one above the other represent the sides of a square, and the single number to their right, represents in inches and decimals, the diagonal of that square. E. g., 54/54 76.37 means that a square the sides of which are 54" would have a diagonal of 76.37".
For determining the length of the long side (hypothenuse) of a right angle triangle, when the other two given sides are not equal, the foot rule, or another steel square may be laid diagonally across the blade and arm, and applied directly to the proper graduations thereon, and the distance between them measured on the rule. If the distance to be measured is in feet, use the 1/12" graduations on the back of the square.
[Illustration: Fig. 194. Face of Steel Square, Octagon, "Eight-Square," Scale.]
To use the octagonal (or 8-square) scale, Fig. 194, which is along the center of the face of the tongue, with the dividers, take the number of spaces in the scale to correspond with the number of inches the piece of wood is square, and lay this distance off from the center point, on each edge of the board. Connect the points thus obtained, diagonally across the corners, and a nearly exact octagon will be had. E.g., on a board 12" square, Fig. 195, find A.B.C.D., the centers of each edge. Now with the dividers take 12 spaces from the 8-square scale. Lay off this distance on each side as A' A" from A, B' B" from B, etc. Now connect A" with B', B" with C', C" with D', D" with A', and the octagon is obtained.