[skidlids]

for a given thread size you use a drill that is the pitch size less than the bolt diameter

so Bolts are usually 8mm X 1.25m, 6mm X 1.0mm, 5mm X 0.8mm etc

8mm tap you use a 6.8mm drill as 6.75mm are very hard to find
6mm tap you use a 5mm drill
5mm.......................4.2mm drill
4mm.......................3.3mm drill

10mm bolts usually come in two varieties on bikes
ISO standard 10mm X 1.5mm so use a 8.5mm drill
and Metric fine 10mm X 1.25mm so use a 8.8mm drill although a 8.7mm drill will be OK
Brake banjo bolts are either 10mm X 1.25 or 10mm X 1.00mm pitch

[Edited on 3-12-2004 by skidlids]