Section 21.9 - Replacement and modification articles(a) If a person knows, or should know, that a replacement or modification article is reasonably likely to be installed on a type-certificated product, the person may not produce that article unless it is-(1) Produced under a type certificate;(2) Produced under an FAA production approval;(3) A standard part (such as a nut or bolt) manufactured in compliance with a government or established industry specification;(4) A commercial part as defined in § 21.1 of this part;(5) Produced by an owner or operator for maintaining or altering that owner or operator's product;(6) Fabricated by an appropriately rated certificate holder with a quality system, and consumed in the repair or alteration of a product or article in accordance with part 43 of this chapter; or(7) Produced in any other manner approved by the FAA.(b) Except as provided in paragraphs (a)(1) through (a)(2) of this section, a person who produces a replacement or modification article for sale may not represent that part as suitable for installation on a type-certificated product.(c) Except as provided in paragraphs (a)(1) through (a)(2) of this section, a person may not sell or represent an article as suitable for installation on an aircraft type-certificated under §§ 21.25(a)(2) or 21.27 unless that article- (1) Was declared surplus by the U.S. Armed Forces, and(2) Was intended for use on that aircraft model by the U.S. Armed Forces.Doc. No. FAA-2006-25877, Amdt. 21-92, 74 FR 53385, Oct. 16, 2009; Amdt. 21-92A, 75 FR 9095, Mar. 1, 2010; Doc. No. FAA-2015-1621, Amdt. 21-100, 81 FR 96688, Dec. 30, 2016