[jliltd]

I'm not sure the physical nut size but I think it's a 10mm metric socket that does the job. They're real easy to see under the truck, right between the front seat and rear seat passengers. They have a metal heat shield held in place by the same nuts. It seems about 90% of the nuts and bolts used in common light maintenance for Toyotas are 10mm wrench size (i.e. dash bolts, ground wire screws, rear oxygen sensor clamps, most body bolts). There are occasional 12mm and 14mm when you move up to oil changes and skid plates. The front Oxygen sensors are 22mm and the spark plugs are standard 5/8" socket.