Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 56
Figs. 119,120. the blade, turning on «, is clamped in position by the thumb-nut h. Fig. 120illustrates a T square wdth a protractor at the head, convenient for laying offlines of designated angles. In many drawing-cases will be found the parallel ruler (Fig. 121), consist- … FiG. 121. 40 DRAWING INSTRUMENTS. ing of two rulers connected by two bars moving on pivots, so adjusted that therulers, as they open, form the sides of a parallelogram. The edge of one of therulers being retained in a position coinciding with, or parallel to, a given line,when the other ruler is…
Mechanical drawing
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