Sprint Fork Stem Nut Size

Hi Everyone,
I want to buy and mount a phone holder to my 2000 955i Sprint ST. When I search Ultimateaddons, I find what I want but it askes me for the Fork Stem Size:


I could take the nut off and measure it but thats is a sclepp, I only want to do that when I fit the phone holder.
Does anyone, know the size off hand? Is it shown above?



Glad for any help here
Dinsdale