Generally divided into gear teeth, tooth grooves, end surfaces, normal surfaces, tooth tip circles, tooth root circles, base circles, and index circles.
  
    
       End face: It is the flat surface at both ends of the gear.
       Normal surface: refers to the plane perpendicular to the gear tooth line.
       Tooth tip circle: refers to the circle where the top of the tooth is located.
       Tooth root circle: refers to the circle where the groove bottom is located.
       Basic circle: The generating line forming the involute acts as a pure rolling circle.
       Industrial circle: It is the reference circle for calculating the geometric dimensions of the gear within the end face.