not sure if the procedure is same between the E70 and E53 but in my case the brackets came with the bolts but there was NO thread in the holes under the seat.

I went to a local hardware store, got appropriate size self-tapping metal screws and attached the brackets to the driver's seat.

http://www.xoutpost.com/880956-post30.html

__________________
E53 X5 4.6iS
147K mi - Sold May 2013
Tireprints left in:
USA, Nicaragua, Costa Rica, Panama, Russia

E53 X5 4.8iS built 2005-10-17
66200 mi - June 2012
96000 mi - June 2013
112000 mi - June 2014
OEM fire extinguisher
OE first aid kit
OE tow hitch
OE TV module
OE aspheric mirror
K&N air filter
black/white badges
rear camera
4-channel video recorder

Here is the list of things I have done to the X