My 7.75" diameter derby covers (most Milwaukee 8 Touring models) require a flat gasket. They are not compatible with the factory, O-ring style gasket.
In my experience, the factory O-ring style is less reliable. These flat gaskets from James have never let me down.
If you're running your factory derby cover, it will have the O-ring style gasket. You'll need one of these to upgrade to my derby cover.
