Heatsink Top:
There are a series of seven 2mm wide crosscuts on either side of the heatsink which have probably been made to improve exhaust airflow at the outer edges. The cross cuts also provide a space for the thermal sensor from the fan to be tucked away. The fins are all smooth faced, and separated 1.5mm apart. Each fin is slightly tapered from the bottom to the top. The lever around the fan swings to one side to lock in a set of spring clips into the HSRM.

Side A:
The aluminum base measures ~11mm thick, and contains a nice copper core. The fins are 30mm tall, and are just 1mm thick. The top portion of the heatsink has a rather larger plastic fan shroud and retention mechanism built into one apparatus. By moving the lever 180 degrees the stainless steel spring clips close in, locking the heatsink pretty securely into the HSRM. The Spire SP411C5 heatsink stands 76mm tall.

Side B:
Here we see another shot of the clip mechanism which is used to lock onto the HSRM. Each corner has a small metal tab which locks into the plastic tab to hold the Spire SP411C5 firmly in place. The outside of the heatsink has a serrated finish, mainly to improve grip.

The cross cuts slice 8mm into the sides of the SP411C5, and after a quick check with the machinists' straight edge we can clearly see that the base has been very well finished. The surface is perfectly flat, and very smooth (a quick test is simply to check if the crystalline structure of the aluminum is visible via some reflected light - and it is). The copper insert is 45mm in diameter, and probably 6-8mm thick. A hole is drilled into the base and the copper plug squeezed in under higher pressure for a good interference fit.