Some parts of the heat sink are directional, and must be put together in sequence. The black gasket is pushed down on top of the white sleeve, with the notch on the gasket facing towards you. This is then pushed inside of the metal heat sink, so that the top of the gasket is flush with the metal heat sink edge, with the notch on the gasket matching the window on the heat sink. The top lid is then placed on, angling the matching notch into the window on the heat sink, and snapped down on the other side. The stem is then inserted into the top of the heat sink assembly.