The Heatsink for HobbyCNC PRO is pre-marked with drilling locations for new assemblies before soldering in the Driver ICs. (red arrows)
Requires drill-and-tap 4-40 in 8 places.
If your driver ICs are already soldered-in, then you will need to mark-and-drill your own hole locations to match your actual installation.
Only one heatsink required per board.
For HobbyCNC PRO boards only.