This International Standard specifies, for narrow V-belts of cross-sections 9N/J (for pulley grooves of effective width 8,9 mm), 15N/J (for pulley grooves of effective width 15,2 mm) and 25N/J (for pulley grooves of effective width 25,4 mm), — the standard effective lengths, — the tolerances on effective lengths, — the centre distance variations, — the conditions for measuring the effective length and the centre distance variation, and — the designation and marking. NOTE 1 The cross-section of a narrow V-belt is defined by a number (9, 15 or 25) followed by the letter N or J to denote single or joined belts. NOTE 2 To define belts of raw-edge cogged construction, the letter “X” is added, i.e. NX or JX.