This is a blue anodized aluminium heatsink, small enough to fit on a stepper driver, but large enough to deliver impressive cooling. It is supplied with double-side thermal adhesive tape.
On the black A4988 Pololu drivers and the purple DRV8825 Pololu drivers, the best location for a heatsink is the underside of the board, just under the chip. Use our tall pin headers instead of the ones supplied with your Pololu driver to rise it above the board it's plugged in, making room for the heatsink and dramatically improving cooling.
Note that, while it's possible to use this heatsink on the underside of the green A4988 Pololu drivers, it works much better on the Black Edition.
Dimensions: 10 mm by 9 mm, and 9.5 mm tall