26 CFR 48.4218-2: -2 Business or personal use of articles.

(a) Business use. Section 4218 applies to the use by a person, in the operation of any business in which he is engaged, of a taxable article which has been manufactured, produced, or imported by him or his agent. For example, a person engaged in the operation of a dairy business incurs liability for tax with respect to a truck body manufactured by him and used in the operation of his dairy business.

(b) Personal use. The tax on use of a taxable article does not attach in cases where an individual incidentally manufactures, produces, or imports a taxable article for his personal use or causes a taxable article to be manufactured, produced, or imported for his personal use.