If you want to do even a simple repair on your microphone, it is good to know that there are two different systems of screws that are used, the US system and the Metric system.
US Machine Screws are described 0-80, 2-56, 3-48, 4-40, 5-40, 6-32, 8-32, 10-32, 10-24, etc. up to 12, and by fractional inch beyond, such as 1/4-20, 3/8-16 and so on. The first number designates a diameter, the second is the number of threads per inch (TPI). Typically the description will also include the length noted as (Example 10-32X1/2.) So the screw size comes first, then an X, and then the length in fractional inches.
Smaller Metric screws are Designated with M and then the diameter in millimeters. Standard sizes are M1, M1.2, M1.6, M2, M2.5, M3, M4, M5 and so on.
Typically the description will also include the length noted as (Example M4X6). So the screw size comes first, then an X, and then the length in millimeters.
There are several common different types of heads. A flathead screws into a countersunk hole, and when screwed in all of the way, the top of the head is even with the panel, a round head is a rounded head that sits above the panel, and a pan head is like the bottom of a pan that sits above the panel. Screws can be slotted, Phillips, TORX or other types, depending on the tool needed to tighten and remove them.