If you are over 1/4 inch in diameter (or 5mm). Drill the hole .020 to .030 inches undersize (.5 to .75 mm).
If you are under 1/4 inch in diameter (or 5 mm). Drill the hole .010 to .015 undersize (.25 to .30 mm).
The closer the drill to the reemed size the tighter the hole will be. Do not run the reemer in and out of the hole only in and flood it. 1/2 the speed and 2 x the feed for highspeed. flood the coolant.