Certain parts of the gear assembly have different part numbers to allow heavy use.
There is a service letter that details the individual parts and their allowable MTOW, if any off the "lighter" parts are installed the entire gear is considered "light"
Even with the "heavy" gear installed the aircraft can only operate at the higher weights if relected in the FM, if not Mr Boeing wants around $100,000 for the paper exercise to allow the higher weight.