These are the only available banded Viton guide seals for Nortons that press on by hand.  Won't dry up oil lubrication to the valve stems like Teflon seals can.  The bands insure a tight seal top and bottom and prevent loosening.  Seals should be used on both intake and exhaust - intake to prevent pulling oil past the guides into the combustion chamber and on the exhaust to prevent spent gasses from blowing past the guides and contaminating the oil.  These seals will fit both the intake and exhaust guides of 750s even if the exhaust guides don't have a groove. For 850s you will have to machine and chamfer the tops of the guides to 1/2".