Tight bolt tolerances vs plastic bushings? To insure the life long integrity of the Fort Knox products, we use tight bolt tolerances. These tight tolerances add to the life of the product. A tight fit of steel to steel will not wear, will stand up better in a fire and give you better long term security than that of the bushings. Plastic bushings require larger holes, will wear over time and we all know what happens to plastic in a fire. Fort Knox builds safes that will surpass the lifetime warranty!