Frank, obviously the amount of thread engagement is critical. MB wheels are hub centered so it makes sense that the hub fits fine. If you're using the 560SEL lug bolts to mount the 500SL wheels check the thread projection on a loose 560SEL wheel and compare it with a loose 500SL wheel. If the thread projection is the same then you should be OK mechanically, but you have a cosmetic problem. I bought E420 wheels for our 1998 E320 and had to purchase new lug bolts. Check with your local MB dealer Parts Department for the appropriate size lug bolts for the 500SL wheels.

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Fred Hoelzle