1.this is our 49cc dirt bike or mini pocket bike cylinder 2.bore size:44mm 3.high quality and best ... size is 44mm.we also have GY6 80cc(47mm),GY6 50cc cylinder kits(39mm) and GY6 60cc cylinder kits(44mm)3 ... 80cc.we supply various kinds of cylinder,such as GY6 50cc,GY6 60,GY6 80 ,GY6 150cc, cylinder assy, scooter ... our porducts,pls feel free to contact to us. mini pocket bike or dirt bike 49cc cylinder