20 Containers, not of metal, for commercial use, namely, cans, boxes, and barrels made of plastic for sampling, packing, storing, or transporting of chemical products and laboratory samples; valves of plastic being other than machine parts; commercial packaging materials, namely, non-metal and non-paper closures for containers, bottles, and bags, and parts thereof and holders for containers, bottles, and bags, and parts thereof to support and fix in an upside-down positions during emptying