link to this site seems to indicate M7 (330ci is same caliper)
http://www.e46zone.com/forum/topic/28853-brake-caliper-bleeder-valve-size/
+ I think M7 x 1.0mm, 32mm long IIRC. 05 Bleeder valve 2 OEM Part No 34116758107.
Why not take the other side nipple out (if you can) and examine thread size as check to be sure.