In every avionics system, Commercial off-the-shelf (COTS) components play an important role by enabling more complex functions. Even in safety-critical systems, COTS hardware components are ubiquitous nowadays. Since the avionics manufacturer do not develop the COTS components themselves, traditional avionics Development Assurance (DA) methods cannot be used. Instead other assurance strategies are used. The problem is that the complexity of the COTS components continuously increase and that several different types COTS components exist, each requiring different assurance strategies. This article includes a literature review over Certification Authority (CA) materials and research reports over COTS hardware components certification related documents since the early 1990s. We then contribute by an approach that can structure this material to provide an overview on COTS assurance methods or activities through an assurance case. The early results show that assurance cases are a possible way to argument COTS assurance and that these cases reveal interconnections between the assurance methods and as such contribute to the overall goal of increased confidence in using COTS components.