Measure oval heads from the largest diameter point-where the dome top meets the conical bearing surface-to the tip. For flat heads, length includes head height. For button, cheese, hex, pan, socket and low socket heads, measure length from under the head. Length is measured the same as inch fasteners, except in millimeters. Comparison of metric and inch fastener sizes. The table below compares various metric sizes to the closest inch equivalent… Table 3. But the M3.5-0.35 has close to double the number of threads per inch of a 6-40, so its threads are very closely spaced (0.014 inches, or 0.35 mm). When you look at fine M14-1.5 and 9/16-18 fasteners, however, the 9/16-18 is finer-it has more threads per inch. (M3.5-0.6 and M3.5-.6 are exactly the same-the '0' is included to make sure that the decimal point isn't missed.)

The same goes for a coarse M3.5-0.6 and a 6-32 screw-the threads of the 6-32 are more widely spaced so, again, it will have fewer threads for the same length. A 9/16-12 screw, which is comparable in diameter and is also coarse, has its threads spaced 0.083 inches, which are farther apart, so there will be fewer threads per unit of measure (we used an inch in the table above). The threads of an M14-2.0 screw, which is coarse, are spaced 0.079 inches (2.0 mm). Comparison of metric and inch fastener threads.

Coarse is the most common metric thread and, as we've mentioned, coarse is assumed when pitch isn't specified. Fine metric fasteners can be more or less fine, depending on size. Coarse metric fasteners, when compared to standard 'inch' fasteners (those commonly used in North America), tend to be less coarse-their threads are more closely spaced-for a comparable size. Metric fasteners are usually classified as either coarse or fine, referring to their thread pitch, although some sizes are available in an extra fine thread.

Fastener thread pitch in millimeters and inches. If you need to know the threads per inch of a metric fastener, first convert pitch from millimeters to inches (multiply by 0.03937), then divide 1 by that number. Inch fasteners are described as threads per inch, which is sometimes mistakenly called pitch. In the example above, a pitch of 1.0 means that from one thread to the next thread, the distance is 1.0 millimeter. If you normally work with inch fasteners, pitch can be a little confusing-pitch is the distance between adjacent threads. (To avoid confusion, we always include the thread pitch for both coarse and fine metric fasteners.) M12 x 25 = 12 mm diameter, coarse thread is assumed (1.75 mm), 25 mm long

Metric bolts sizes m1.6