This 49cc 50cc crankshaft is designed for 4 stroke GY6 139QMB 139QMA engines.It features a stroke of 57.8mm and an overall length of 285mm.The flywheel thread size is M12x1.25 with a thread length of 14mm.The drive end thread size is also M12x1.25 with a thread length of 14mm.It has an inner diameter (piston pin hole) of 15mm and includes 19 splines.Main bearings are included with a size/model of 22 X 56 X 16 [63/22/P5]. Compatibility Disclaimer: This is an aftermarket replacement part.Any brand names or model designations mentioned are used solely for the purpose of demonstrating compatibility.