Here's a photo of a correct lug bolt for a stock BMW wheel. This one is chrome plated, while most BWM bolts are black oxide finished. The conical seat is very clear. A spherical seat bolt has a "rounded" surface where this one has a flat conical taper.
For more on wheel and tire changing that is specific to the X3(F25) see:
http://x3.xbimmers.com/forums/showth...hanging+Wheels