Section 18 Optical, photographic, cinematographic, measuring, checking, precision, medical or surgical instruments and apparatus; clocks and watches; musical instruments; parts and accessories thereof 91 Clocks and watches and parts thereof 91 11 Watch cases and parts thereof 91 11 10 Cases of precious metal or of metal clad with precious metal Commodity Code Description 91 11 10 00 Cases of precious metal or of metal clad with precious metal