Characterization of the Subsystems in the General Three-System of Screws

The chapter examines the subspaces of a space spanned by three twists (or wrenches) with finite pitches and linearly independent directions. The main result is the complete characterization of all cylindroids nested within a general three-system of screws. The findings are illustrated by means of the prestereographic model of three-dimensional projective space, which allows to faithfully represent the screws of a three-system, with their pitches and axis locations, by the surface of a sphere