ODSEVEN Mini Aluminum Heatsink for Raspberry Pi - 13 x 13 x 3mm
This heatsink is made from high quality aluminum and will work perfectly with any Raspberry Pi but is best paired with a Raspberry Pi 3 since it can run a little hot. It comes with thermal adhesive already applied to the back making installation super easy. Clean the surface of the chip of any dust or grease then peel off the protective film and press the heat sink firmly onto the chip.
We don't have formal specs for this heat sink, but when we ran 'stress -c 4' on the Pi 3 to run all 4 CPUs, a heat-sink-less Pi quickly dropped down to 0.96 GHz to maintain thermal equilibrium. With this heat sink installed, it could run at 1.02 GHz (so, 6% higher performance). It's a very minimal heat sink!
Note that you do not need a heatsink for the Pi 3, it will automatically adjust its speed to avoid overheating! It can also, of course, be used for other processors and chips.