The #6-32 UNC is a UTS screw specifying a major thread diameter of #6 which is defined as 0.1380 inches (3.51 mm); and 32 tpi (threads per inch) which equates to a thread pitch of 0.031250 inches (0.7938 mm).
You can identify an M6 screw by measuring the diameter with a ruler. It'll be 6 mm, or slightly more than 7/32 inches (0.228″).
The tap drill size for M4 is 3.3 mm and 2.85 mm for UNC 6-32. The major diameter (thread size) for UNC 6-32 is 3.505 mm (according to the Maryland Metrics Thread Data Charts).
Screws have three basic measurements: gauge, threads per inch, and shaft length in inches. So, you may also see a measurement like 6-32 x 1 1/2". This means it's a #6 diameter, with 32 threads per inch (almost double the normal thread count as a standard wood screw) and an inch and a half long.
The bigger the number the bigger the screw. The second number is the number of threads per inch.
A 6–32 means a threaded fastener bolt that is size #6 and 32 threads per inch. A clearance hole will pass the threaded portion of the bolt. A tap drill is less than the thread size and used to accept a threading tap that will thread the hole to take a #6–32 threaded screw..
The M4 machine screw has a thread diameter of 4 millimetres, in simple terms the M stands for millimetres followed by the size – in this case 4 mm.
Standard metric screw dimensions are determined by the pitch and the major diameter, which as the illustration shows, is the largest diameter of the screw. Let's say it's 4mm, in which case it appears as M4 (the M means metric).
In summary, 6/32 inches is the same as 0.1875 inches and 6/32 inches is also the same as 0.015625 feet.
A: Everbilt #6-32 x 2 in. Phillips Flat Head Stainless Steel Machine Screw (20-Pack) has a shaft or screw length of 2".