Section 18 OPTICAL, PHOTOGRAPHIC, CINEMATOGRAPHIC, MEASURING, CHECKING, PRECISION , MEDICAL OR SURGICAL INSTRUMENTS AND APPARATUS; CLOCKS AND WATCHES; M USICAL INSTRUMENTS; PARTS AND ACCESSORIES THEREOF 91 Clocks and watches and parts thereof 91 11 Watch cases and parts thereof. 91 11 10 91 11 10 00 Commodity Code Description 91 11 10 00 00 - Cases of precious metal or of metal clad with precious metal 91 11 20 00 00 - Cases of base metal, whether or not gold- or silver-plated 91 11 80 00 00 - Other cases 91 11 90 00 00 - Parts