Gearbox filler plug

Hi -all. I'm in the middle of a full service and want to drain and refill the gearbox, the filler plug looks like a torx bit, i've tried a 50 and 55 mm bit but neither seem to fit the 50 seems to small and the 55 seems to big. Can anyone confirm that it is a torx bit and also the size.
The Disco's a 95 300TDI.

Just done the obvious and had a look in the haynes but can't find any info in there.. I know a man who would know but he's on holiday so i'mstuck there i'm afraid.

just done that job meself its a t55 torx i had to buy one bout 4 inches long the saw off about 3 inches but it done the job steve