what size is the gearbox oil filler allen key

anyone know off the top of their head what size allen key I need to remove the gearbox oil filler plug?

thanks.

 

17mm

 

seconded 17mm, make sure you can undo the fill plug before you undo the drain plug

 

just had replacement g'box fitted with new oil, just wanted to check the level for my own piece of mind.
ta fellas.