19 C.F.R. § 10.134
A showing of intent by the importer as to the actual use of imported merchandise shall be made by filing with the entry for consumption or for warehouse a declaration as to the intended use of the merchandise, or by entering the proper subheading of an actual use provision of the Harmonized Tariff Schedule of the United States (HTSUS) and the reduced or free rate of duty on the entry form. Entry made under an actual use provision of the HTSUS may be construed as a declaration that the merchandise is entered to be used for the purpose stated in the HTSUS, provided the Center director is satisfied the merchandise will be so used. However, the Center director shall require a written declaration to be filed if he is not satisfied that merchandise entered under an actual use provision will be used for the purposes stated in the HTSUS.
19 C.F.R. §10.134