This International Standard specifies the principal characteristics of grooved pulleys (for groove sections 9N/J, 15N/J and 25N/J) intended to take both single and joined narrow V-belts for industrial power transmission drives. Some background information on the series of effective diameters is given in annex A. NOTE The effective width of a groove is regarded as the basic dimension of standardization in the effective system for grooves and for the corresponding narrow V-belts considered as a whole.