Determining drill size for panel mount components
Amazingly, there is actually a standard that defines what should be the hole sizes to accomodate standard threaded screws. It is ASME B18.2.8-1999: &quot;Clearance holes for bolts, screws and studs&quot;. There is a similar ISO standard as well (for metric only): ISO 273-1979. For each thread size, they give three hole diameters (for close, normal, and loose-fit categories).
Here is a PDF containing the chart, but you can easily find them using the &quot;hole clearance chart metric&quot; search terms on the internet.
In your specific case, for M7, it is 7.4mm for close fit, 7.6mm for medium, and 8mm for loose fit. You choose.