Here is a quick guide to PCB drill sizes for common screw or fastener sizes used for mounting PCBs, M3 for example.
The table does NOT list the recommended clearance around the drilled hole. You may choose to use any clearance diameter depending on your application.
| S. no. | Screw/Fastener Size | PCB Drill Size |
| #1 | M1.6 | 1.8mm |
| #2 | M2 | 2.4mm |
| #3 | M2.5 | 2.9mm |
| #4 | M3 | 3.4mm |
| #5 | M4 | 4.5mm |
| #6 | M5 | 5.5mm |
| #7 | M6 | 6.6mm |
References
Reference 1: Metric Clearance Hole Chart, Full