This listing is for a pair of Norton 850cc Commando piston kits  @ +0.040"   (78mm)  Standard size is 77mm making these 1mm oversize. Although these are boxed in MCA boxes they are made by GPM and are original equipment now supplied by Andover Norton. GPM rings are far superior to cheaper alternatives and the oil control is a 2 piece with a spring expander. We offer a reboring service aswell as our world famous exhaust thread repair for both Triumph and Norton. Please find us and follow us on Facebook to see our full engineering service @ Seager Engineering