[SteveAustin]

Triple-clamp Crown Nut. Looks like 36mm, but I don't own a '19, so don't take that as fact. It doesn't have a lot of torque on it, a large adjustable should work if you can't find a socket, but be careful with an adjustable, use a rag between the tool and the nut and be sure the adjustable is tight.

When I say 'adjustable', I mean 'Crescent' with the thumbwheel to open/widen or tighten/close. NOT 'channel locks' or 'Vice-Grips'.