Dr. Pulley 16x13 Round Roller Weights (5g) Dr. Pulley 16x13 Round Roller Weights for 50cc 4-stroke QMB139 engines. Please select weight from drop-down menu. Dr. Pulley Round Roller Weights have exceptional durability, heat resistance and are low friction and low wear.Please see our Warranty & Returns Policy. Size: 16x13 Set of 6 Lasts longer than standard roller weights Excellent Heat Resistance Low Friction / Low Wear