I measured the sizes and got the following: small: 15 teeth; d(hole)=4mm; L1=3mm; D=6mm; L=7.5mm; OD=8.25mm; large: 30 teeth; d(hole)=4mm; L1=3mm; D=12mm; L=7.5mm; OD=15.4mm; But I am satisfied. In addition, the seller sent two pairs of gears instead of one, which I am very pleased.