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 20 - Cases of base metal, whether or not gold-or silver- plated Commodity Code Description 91 11 20 00 - Cases of base metal, whether or not gold-or silver- plated