What Size Is Front Drive Sprocket Nut On 1200cc Bonneville's

I plan on replacing the chain and sprockets on my Bonneville Speedmaster and want to make sure I have the right tools. Anyone know what size the nut is for the front sprocket? It's part T1180175 which is used on all the 1200cc bikes and others. The sprocket is actually hidden behind read brake and coolant gubbins and I would prefer not to take things apart just to measure it's size.

 

Thanks, that's a different part so may not be the same size. According to what I find online as well the the 1200cc engine my parts used on the T100 engine and Steep Cup/Scrambler.

I have a 38mm socket I bought for the steering head, after I got a 37mm that the Haynes manual said was the correct size for T120/Bobber (manual didn't cover my Speedmaster). If I don't find out the correct size, I may splash out on a set of big sockets to make sure I've got things covered.

 

Many thanks. I'll buy a 36mm then, as I have a 37mm. (With 160Nm torque I want something that's as good a fit as possible).