(1) Since the rack tooth profile is a straight line, all points on the tooth profile have the same pressure angle, which is equal to the inclination angle of the tooth profile. This angle is called the tooth profile angle, and the standard value is 20 °.
(2) Any straight line parallel to the addendum line has the same pitch and modulus.
(3) The straight line parallel to the tooth top line and with the tooth thickness equal to the tooth slot width is called the dividing line (centerline), which is the reference line for calculating the rack size.
