The inner diameter of the cylinder is 50mm, with four locating pins The length of cylinder head and valve cover is 69mm, not 64mm. Fit GY6 50cc to 100cc 139QA 139QMB Engine Intake pipe screw, exhaust pipe screw, exhaust pipe nut, exhaust pipe pad Please carefully check the appearance, size, shape, product description of the goods before purchase, and compare with the original goods, thank you.?? Product description 50mm caliber cylinder head kit with 69mm valve scooter Taotao and Ma ATV mopopies for GY6 50cc to 100cc engines