This has replaced hobbing for some involute gears and cutting external splines and slots. The evolute of an involute is the original curve. The vane geometry may be involute, archimedean spiral, or hybrid curves. Furthermore, those "involute bevel gear sets" cause more noise. Furthermore, the "involute bevel gear sets" cause more noise. This diminishing radius produces a series of involute midpoints (i.e. located on a spiral). Spur gear teeth are manufactured by either involute profile or cycloidal profile. "Strionautilus" is compressed, involute, with fine longitudinal striations. In the 18th century involute gears, another mathematical derived design, came into use. The base diameter of an involute gear is the diameter of the base circle. For this reason, nearly all modern gear teeth bear the involute shape. For every pair of conjugate involute profile, there is a basic rack. It begins to involute with contractions of the smooth muscle of the uterus. It varies continuously along the involute profile. In contrast to RICH, NICH does not involute and rarely ulcerates.