The Heatsink Fan:
The Cooljag OAK-H2 heatsink is built with a 93mm diameter fan. The 7-bladed impeller on this Pulse Width Modulation (PWM) fan spins at 1800-3500RPM when controlled by the computer's BIOS, but when running on a standard 3-pin fan header defaults to a slow speed that seems more like 600-1800RPM. Power is supplied by the 4-pin PWM fan cable which connects to a standard 3-pin or 4-pin motherboard fan header. If you short the blue and yellow pins of a 4-pin PWM fan it will automatically spin up to its maximum RPM as the PWM signal is overruled. For this heatsink, this tweak is highly recommended.

Heatsink Top:
The copper cooling fins are directly below the fan blades, so they should be getting a good solid blast of cool air. The central copper column is 33mm in diameter, hollowed out, and has had its' inside coated black. Each copper fin is 0.4mm thick and spaced 1.0mm apart at the base. The tips are spaced ~2.5-3.0mm apart. A low profile black plastic fan shroud supports the fan and doesn't block in the central void (where heat buildup will occur). The rear of the fan is flush against the plastic support frame, which is unfortunate as it prevents sufficient airflow from occuring behind the fan motor. The body of the heatsink is 89mm across.

Heatsink Side B:
The plastic fan shroud directs airflow down about 23mm through the cooling fins before allowing it to escape. After which, the warm air exhausts outwards in all directions where it cools adjacent board-mounted components. Most socket 775 Intel motherboards are designed to use this source of airflow, and so VRM and chipset heatsinks are often entirely passive.

Heatsink Base:
The copper base of the Cooljag OAK-H2 heatsink measures 36mm round, but only 29mm of it is useable for making contact with the processors' integrated heatspreader (IHS). The copper is machine turned flat, and quite smooth. Surface roughness is on the order of ~16 microinches, which is considered very good. Note how much of the cooling fins are obscured by the steel mounting clip - there is some clearance given, but we have to wonder if Cooljag could have opted for a better clip here.