Over the years I've discolored plenty of chrome and just as many nonchrome nuts and bolts by bearing down just a little too hard. It reached the point where I was all set to buy one of those plastic-lined socket sets when one of my custom bike-building buddies turned me onto a simple trick. After the bolt or nut (as the case may be) is run down but before it's fully tightened, my buddy throws some duct or electrical tape around the fastener's flats. The tape prevents the hardware's finish from damage and discoloration, and as a bonus it practically eliminates any chance of the wrench slipping off the fastener, an important consideration for those instances when only an open-end wrench will work. Alternatively, you can wrap the wrench jaws with tape. I just can't believe I didn't come up with this one on my own!