A "bezel" or mounting ring as it is commonly called is a ring or surround that is used to mount the pickup for height adjustment. Mounting rings are very common in Gibson instruments and allow you to balance the output from neck, middle or bridge pickups. I usually adjust the pickups by first pressing the two outside strings at the last fret and adjusting the pickups as follows: The bridge pickup is adjusted 1/16" inch on both treble and bass side. The neck and middle pickups (if available), I adjust 1/16" inch on the treble side and 1/8" inch on the bass side.