This International Standard specifies, for classical and narrow V-belts of sections Y (for groove profile with datum width 5,3 mm), Ζ (for groove profile with datum width 8,5 mm), A (for groove profile with datum width 11 mm), В (for groove profile with datum width 14 mm), С (for groove profile with datum width 19 mm), D (for groove profile with datum width 27 mm), Ε (for groove profile with datum width 32 mm), SPZ (for groove profile with datum width 8,5 mm), SPA (for groove profile with datum width 11 mm), SPB (for groove profile with datum width 14 mm), SPC (for groove profile with datum width 19 mm): — the recommended datum lengths; — the tolerances for datum lengths; — the centre distance variations; — the conditions for measuring the datum length and the centre distance variation. The V-belts of sections Y, Z, А, В, C, D, Ε are called classical V-belts and those of sections SPZ, SPA, SPB and SPC are called narrow V-belts. It is important that narrow belts are not used with pulleys uniquely designed for classical belts.