An Allen key M4 is a 2.5 mm hex key.
This size is commonly used for M4 screws and bolts, which are small fasteners often found in electronics, furniture, and other applications.
The number "4" in "M4" refers to the nominal diameter of the screw or bolt in millimeters.
The corresponding Allen key size for M4 fasteners is 2.5 mm, which is the size of the hexagonal hole in the Allen key.
This means that a 2.5 mm Allen key will fit perfectly into the hex socket of an M4 screw or bolt, allowing you to tighten or loosen it.
