National standard v-belts of the type o, a, b, c, d, e, f, seven models, there are three pulley Groove angles of 34 °, 36 °, 38 °, corresponding to each type of v-belt and provisions of the each angle of the v Groove small minimum diameter of pulley, pulley is not specified. Belt round of slot angle is divided into 32 degrees 34 degrees 36 degrees 38 degrees, specific of select to according to with round of slot type and benchmark diameter select; belt round of slot angle with belt round of diameter has relationship, different model of belt round of slot angle in different diameter range Xia of recommended belt round slot angle number following: O type belt round in with round diameter range in 50mm~71mm Shi for 34 degrees; in 71mm~90mm Shi for 36 degrees, >90mm Shi for 38 degrees; A, type belt round in with round diameter range in 71mm~100mm Shi for 34 degrees, 100mm~125mm Shi for 36 degrees; >125mm Shi for 38 degrees; b type belt round in with round diameter range in 125mm~160mm Shi for 34 degrees; 160mm~200mm Shi for 36 degrees, >200mm Shi for 38 degrees; c type belt round in with round diameter range in 200mm~250mm Shi for 34 degrees, 250mm~315mm Shi for 36 degrees, > 315mm for 38 degrees; d-type pulley pulley diameter is 36 degrees when the 355mm~450mm, >450mm to 38 degrees; e-500mm~630mm to 36 degrees, >630mm to 38 degrees.