With regard to the spacers that are mentioned above in post #2, they may be thought of as adjusters of the wheel's ET. In this case the wheel as manufactured by MB is ET49, with the spacer added the offset becomes ET30.

The spacer is 19mm thick, and is a light press fit into the wheel.
The bolts are 2 5/16" (58.7mm) long, measured from the bottom of the ball to the end of the threads. That bolt length, in combination with the wheel in question, and the spacer, yields an exposed thread length that equals the OEM.

http://www.peachparts.com/shopforum/sl-forum/378988-hubcentric-wheel-adapters.html