2005 Nissan Xterra Rear Differential What Is The Hex Socket Size To Remove The Plug In A 2005 Nissan Xterra Rear End Axle.?

What is the hex socket size to remove the plug in a 2005 Nissan xterra rear end axle.? - 2005 nissan xterra rear differential

The pinion seal is leaking my wife's Nissan Xterra and I need to add oil rear differential. It is a card that will be removed from a hexagonal type A plug must. Someone knows how big and if it is metric or SAE? Thank you in advance. John.