{"data":{"fields":"term_definition","term_definition":"<div class=\"definition\">The involute of spur gears, helical gears and worms are those in which the active portion of the profile in the transverse plane is the involute of a circle. As mating teeth slide and roll through mesh, the progressive points of contact between involute teeth always lie along a straight line of action. Tooth contacts from the beginning of mesh to the line of centers take place within what is called the angle of approach. Tooth contacts from the line of centers to the end of mesh take place within what is called the angle of recession.<\/div>"}}