What is "tangent screw"

Tangent \Tan"gent\, a. [L. tangens, -entis, p. pr.] Touching; touching at a single point; specifically (Geom.) meeting a curve or surface at a point and having at that point the same direction as the curve or surface; -- said of a straight line, curve, or surface; as, a line tangent to a curve; a curve tangent to a surface; tangent surfaces.

Tangent plane (Geom.), a plane which touches a surface in a point or line.

Tangent scale (Gun.), a kind of breech sight for a cannon.

Tangent screw (Mach.), an endless screw; a worm.