This starter idler reduction gear set is designed for the CB250 250cc air-cooled engine.The small double gear features a 15-tooth small gear and a 17-tooth larger gear.The large double gear consists of a 21-tooth small gear and a 61-tooth larger gear.The connecting rod has an overall length of 45mm and a diameter of 10mm.This item serves as a functional replacement to restore engine starting performance.Please verify the tooth counts and dimensions against your existing parts before purchase to ensure compatibility.The package includes one set of starter idler reduction gears.Professional installation is recommended.