Tools for cutting male and female screw threads
The guide for the male screw is straight and right-angled (a n); the female's must be acute (m o)
The note beside the figures explains how to shape the guide-tools for cutting screws: the tool that works the male screw can be straight with a right angle (shown at a n), while the tool that cuts the female thread must have an acute angle (m o) so that it touches the hollow of the female at a single point; being round, the male too touches its tool at a point. The drawings show two long tapered cutting tools, a large vertical screw held in a rectangular frame, and, below, a screw-cutting apparatus with a cylinder and a wheel pierced with holes for indexing.
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Right-angled tool for the male, acute for the female
The guide-tool that works the male screw can be straight and set at a right angle, as shown at a n. The tool that makes the female thread must instead have an acute angle, as shown at m o, because it has to touch the hollow of the female at a point; and the male, being round, likewise touches its tool at a point.
Screw press and indexing wheel
A large vertical screw is held within a rectangular frame at the right of the sheet. Below, a screw-cutting apparatus is drawn with a horizontal cylinder and stacked discs beside a wheel pierced by a ring of holes, apparently for indexing the cut.