Gearbox sprocket available in 17, 18 or 19 teeth for all carburettor 3/4 cylinder carburettor models, all 955 and all 1050 models. Smaller than standand gives improved acceleration at the expense of fuel consumption and on some models increased chain guide wear. Larger than standard engine sprockets lose out slightly on acceleration but have a more relaxed feel in top gear. Sprockets have side damping bonded rubber. (530 chain size).