When it comes to drilling a pilot hole into a piece of wood or metal to which a screw will be sunk, amateur craftsman may simply drill a hole with a drill bit that roughly resembles the size of the screw. There is, however, a strict method to calculating the correct size of hole to drill. Drilling the proper-sized hole will ensure the screw fits perfectly, providing a correct fit.
Read the packaging on the screw that you plan to use and understand its terminology. If it's an M2 thread screw, this means that it's measured in the metric method, rather than the imperial or U.S. method. An M2 screw is the second-smallest standard size of metric screw. The M2 designation is derived from a highly complex mathematical formula that involves the relation between the depth of the thread, the angle of the thread and the angle of the "V" shape between threads.
Consult a metric thread and tap size chart or booklet. These charts or booklets are commonly sold at hardware stores and contain a wealth of information about metric threads and how they relate to tap sizes. There is a unique tap size that corresponds with each size of metric thread.
Find the listing for an M2 thread and look up the tap drill diameter size for that size of screw. In the case of an M2 thread screw, the tapping diameter is 1.6 millimetres.
Select a metric drill bit measuring 1.6 millimetres and drill the pilot hole. Once the hole has been drilled, screw the M2 thread screw into the hole. Because the hole has been sized correctly, the screw will fit perfectly.