Does anyone know what the size of the bolt is for the gear shift knob on a w124 is?

I was trying to fit my new adaptor shaft onto it and I could not get the darn bolt off! (Probally because I had the wrong wrenches. )

Could I get the wrench at home depot?
I money wrench will not fit in the small space!

I almost got too impatient and started to strip the nut! Goo thing I stopped before it was too late!

Thanks!

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2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)