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"Where the head is movable, the pivot should be quit large, and the hole in which it plays be bushed with metal; the washers must be large, and the clamp screws of hard metal, with deep threads and unreliable." —Grimshaw, 1902

Taper Head Adjustable T Square Side and Front View

"Where the head is movable, the pivot should be quit large, and the hole in which it plays be bushed…