The TI-RV108N is an extruded aluminum heatsink, but there are several differences between it and what most of us are used to seeing. For starters, the main components of the heatsink, the fins, are all very thin - typically no more than 1mm thick.

The copper core which measures 28mm in diameter forms the contact area of the heatsink, and through an interference joint with the surrounding aluminum transfers whatever heat it absorbs out to the many thin aluminum fins.

The fins branch out to a length of ~27mm with a slight clockwise curve from the main "X-Form" arms which are about 2.5mm thick. For the heatsink to be efficient, the large arms which form the X pattern must be thick enough to transfer the heat energy out to the corner fins.