Mercedes W126 wheels on a W123 - What Lug Bolt to Use?

Hey, quick question. I've scoured the internet and can't find a definitive answer. Someone here must know.

I'm mounting a set of W126 15" alloy wheels onto my W123. The W123 currently has a set of the 14" Bundt wheels. When I went to bolt on the W126 wheels last night, using the same wheel bolts, they only protruded about 3/8" past the wheel mounting face- not enough thread engagement to be safe. The same stud protrudes about 3/4" through the Bundts.

I need a lug stud that's about 10 to 15 mm longer than the ones I have now. What stud should I be using?

Thanks!

What about W126 lugs? Or look up the complete specs on W123 lugs, then find some longer?

A complete set of lugs adds significantly to the cost of the wheels.

Rock auto to the rescue, the list a Dorman part number 610247 that fits both W123 and W126, it's 10mm longer than the standard stud/bolt.

Nope, those are wrong. I measured the lugs on the car now and the thread length is 29mm, which is too short for the W126 15" wheels. The 2nd gen W126 had these wheels, from 1986-1992-ish. This is part of the problem with looking up lugs by vehicle type. There were also steel wheels available.

I finally found a seller on ebay who listed the thread length of the bolts they were selling specifically. Looks like the ones I need have a 40mm thread length. Again, this was confusing as bolts were advertised using overall or thread length, without really what they were referring to.

I ordered a set of the 40mm thread length bolts, should be here on Monday, and not horribly pricey - about $30 for the set of 20.

The Mercedes P/N for these lug bolts/ wheel bolts is: P/N 126 400 00 70