The only way to overlay a 3x112 and a 5x112 bolt circle is to share one hole, which is exactly how ours are made. Incidentally, we originally tried to use a 4x100 pattern, then a few other four bolt (4x114.5? I think??) before finally going with the 5x112 pattern. (Again, because there was no way to overlay the bolt circles without overlapping on some of the counterbores.)
Besides, 5x112 lets you use OEM Benz wheels, which really seem to suit the car well.
So, yes our adapters have a "shared hole" with a longer lug bolt that passes through the wheel and adapter and threads into the hub. Generally we suggest that you just buy a set of locking lug bolts for that longer bolt, as they come in sets of four and keep bad people from stealing your bling. In most cases we've seen so far, stock Mercedes wheel bolts have been good for the four "shorter" bolts per wheel. (And of course, we include the special socket head cap screws that bolt the adapter directly to the hub.)
We have a pretty thorough write up on our site regarding how they install, perhaps that might make it all clearer. (A picture being worth 1000 words and all..)
Smartparts
Cheers,
Johnny
Oh, and BTW, I was sort of troubled that the original post inferred that there was something sketchy about my eBay ID... While it's true that I have changed my user "nickname" twice in about 10 years of selling, (once at eBay's insistence because my original nickname was an email address, and then again just recently to match the name of our new company), I think that my 100% favorable feedback over those 10 years, including glowing praise for my honesty and integrity as a seller (go ahead, read it]) are probably more relevant than changing nicknames twice. I'm a lot of things, but "sketchy" ain't one of them. Thanks for letting me vent; my reputation means a lot to me..