Adapter caps for sample collection containers have a monolithic elongate body with an upper neck portion that merges into a larger lower body portion with an open internal cavity. The upper neck portion has an open needle bore that is concentrically aligned with the open internal cavity. The monolithic elongate body has an axially extending centerline. The needle bore has a downwardly extending wall with an inner surface that comprises a plurality of circumferentially spaced apart longitudinally extending flat surfaces.
