FIX-3.5-15 is a fastener specification provided by the Aerospace Industries Association (AIA) for fastening components together. The specification outlines the material and thread characteristics required for each fastener, including overall length, diameter, thread pitch, major and minor diameter, head type, thread form and shape, thread engagement, and surface finish. Additionally, it specifies the required minimum proof load. This specification is widely used in the aviation industry, as well as general mechanical applications.