It's pretty standard. BMWs have lug bolts, not lug nuts. So, when you remove them there are no bolts supporting the wheels. There is a small lip on the hub that will keep the wheel from just dropping off. Putting the wheels on is slightly more challenging, because you have to get the holes lined up accurately.
Present - '06 E90 330i sport; Past - '04 E46 ZHP, '00 E46 328i
www.bmwcca.org member #388003 - Use me as a referral & you could win a one day ///M Driving School!!