PREFACE TO TWELFTH EDITION. 



This edition introduces much new matter thought useful, and 

 revises, to a considerable extent, the data of the prior edition, 

 to conform to current practice and a wider range of structural 

 products. 



The table of steel ingots is greatly amplified by the addition of 

 more sizes and styles. 



Cuts and properties of many new sections are introduced, 

 among which are bulb angles, top-guard bulb angles, 3-inch and 

 4-inch channels for cars, 12-inch ship channels, and some 

 seventeen T-bars of considerable range in dimensions. 

 Three sizes of rolled steel car stakes are also included. 

 Drawings and tabulations of standard ship sections including 

 ship channels, bulb angles and one Z-bar hatch section, to- 

 gether with the equal leg and unequal leg angles selected as 

 standards for ship building, which were adopted on November 

 20, 1918, are now given. 



Rolled safety floor plates and buckle plates are newly listed 

 in most convenient sizes. 



In view of well- recognized practice, the standard connection 

 angles formerly shown have been superseded by new standards 

 and all tables relating thereto are correspondingly modified. 



Additional new tables believed of value have been incor- 

 porated. These refer to Flat and Corrugated Steel Sheeting; 

 Roof Truss Dimensions and Stresses; Moments of Inertia of 

 Rectangles; Sizes of Wrought Spikes and Wood Screws; Wire 

 Gauges shown in Combined Table; Decimal Equivalents of Non- 

 Binary Fractions; Square Roots and Cube Roots of Fractions; 

 Weights of Circular Steel Plates; Trigonometrical Formulse; 

 Squares and Cubes of Numbers and Fractional Intervals; Com- 

 binations and Factors of ir\ Relations in Circular Segments; 

 Volumes and Surfaces of Solids; Minutes and Seconds expressed 

 in Decimals of a Degree and vice versa; Metric and Customary 

 Measure Conversions, etc. 



The tables of weights for various substances and materials 

 have been considerably augmented. 



Specifications for Structural and Boiler Steel have undergone 

 slight revision to bring these up to date. 



