In one example, parts to be assembled into a fluid flow structure include: a first part having flat sealing surfaces each surrounding one of multiple first conduit openings; a second part having sealing ridges each surrounding one of multiple second conduit openings; and a single gasket having multiple holes each surrounded on both sides by a flat sealing surface. Each hole in the gasket is positioned to align with one of the first and second conduit openings so that, when the parts are assembled together, each gasket sealing surface contacts a corresponding one of the flat sealing surfaces on the first part or the sealing ridges on the second part and fluid may flow through the holes in the gasket from the conduit openings on one of the parts to the conduit openings on the other part.