26 C.F.R. § 48.4218-4
For purposes of section 4218 and § 48.4218-1 , an article is used as material in the manufacture or production of, or as a component part of, another article, if it is incorporated in, or is a part or accessory of, the other article. Lubricating oil in the crankcase of a new truck is an example of a taxable article use as material in the manufacture or production of, or as a component part of, another article. In addition, an article (other than gasoline used as a fuel) is considered to be used as material in the manufacture of another article if it is partly or entirely consumed in testing such other article; for example, shells or cartridges used in testing new firearms. similarly, if an article is partly or wholly consumed in quality testing a production run of like articles (as, for example, an automotive part destroyed in stress testing) such article is also considered to have been used as material in the manufacture of another article. However, if a taxable article that has been used tax free and only partly consumed in testing is later sold, or put to a taxable use, by the manufacturer, tax attaches to such sale or use. An article that is consumed in the manufacturing process other than in testing, so that it is not a physical part of the manufactured article, is not used as material in the manufacture or production of, or as a component part of, such other article. Thus, lubricating oil consumed in operating plant machinery in the course of the manufacture of automobile truck chassis is not used as material in the manufacture or production of, or as a component part of, the truck chassis.
26 C.F.R. §48.4218-4