Abstract: An endless power transmission belt construction, a rotatable pulley therefor, a combination of the belt construction and pulley and methods of making the same are provided, the belt construction having opposed side edges and having an inner surface defining a plurality of longitudinally disposed and alterntely spaced apart like projections and grooves for meshing with an outer peripheral ribbed surface of a rotatable pulley, each projection of the belt construction having a generally V-shaped transverse cross-sectional configuration defined by two substantially straight side edges that converge from the respective apexes of the grooves of the belt construction that are on opposite sides of that projection to an apex of that projection, the side edges of each projection of the belt construction defining an angle of approximatly 60.degree. therebetween with the thickness of the belt construction being substantially the same as the thickness of a similar belt construction wherein the angle is approximately 40.