Excerpt from Instruction Paper: Subject: Mechanical Drawing It will be noticed that the width of the thread and of the groove, measured parallel to the center line m n, and the depth of the thread, are all exactly the same; that is, they are each equal to one-half of the pitch. If a section were taken through the center line ma, the thread and groove would look like Fig. 71, a series of squares hence the term square thread. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.