Section 18 Optical, photographic, cinematographic, measuring, checking, precision, medical or surgical instruments and apparatus; clocks and watches; musical instruments; parts and accessories thereof 90 Optical, photographic, cinematographic, measuring, checking, precision, me Thereof. 90 20 Other breathing appliances and gas masks, excluding protective masks having neither mechanical parts nor replaceable filters Commodity Code Description 90 20 00 Other breathing appliances and gas masks, excluding protective masks having neither mechanical parts nor replaceable filters.