Premium Continuously Variable Transmission CVT Drive Belt Replace Part Number: 669-18-30, 669 18 30 Fits 49cc 50cc GY6 QMB139 4 Stroke Engines Outer circumference: 669 mm ( 26.3 inch), Top width: 18 mm ( 0.7 inch), Pitch: 30 degree Good performance: Oil and heat resistant, high mileage and reliable performance ow to Select the Correct Comet Belt 1.Determine the Series Type 2.Measure the “Outer Diameter” (O.D.) of the driven pulley on the jackshaft. 3.Measure the “Center Distance” (C.D.); which is the exact distance between the center of the engine crankshaft and the center of the jackshaft. Must be precise. 4.Use the two measurements; the driven pulley outer diameter and center distance measurement to determine the correct belt part number from the relevant chart below. Note: Should your machine’s center distance fall between the center distance (C.D.) settings listed here, select from the two belts the one with the larger outside circumference (O.C.) for best wear and to avoid machin