how do I know what size lugs to use?




[moved from w203 forum]
okay, another dumb question from eddieo; please be nice.
I bought some wheels and snow tires for the 203 coupe. I went with these 16's that came off someone's SLK:

The seller gave me a bunch of lugs with them and stated that on his car, he needed to use different size lugs on the back (I hardly paid attention, figuring my mechanic will sort it out). My OEM 17" wheels, Evolution, I believe, are these:
...and the lugs for these OEM wheels are not only wicked long, but have a good half inch with no threads, as the alloy is really thick.
When we put the wheels on the car (my mechanic was on vacation, so one of his helpers put them on for me), we used the original, long lugs, and the rear wheels locked up completely (wouldn't turn with car in gear). We tried the new, short lugs, but still had a scary scraping noise. Turns out we had knocked a spring off the brake (parking brake mechanism, maybe?). After we pulled the caliper and rotor, fixed the spring, and then tried the new short lug again, we still had a nasty noise, so for now, I've got one pair of each tire and wheel on the car (unfortunately, the snows are on the front, where the wicked long lugs didn't seem to make a difference). I'm hoping all I need to correct this debacle is the right size lugs, but how do I know what length, and where's a good place to get 'em? Thanks.















