Manufacturers interested in supplying their products
globally are being urged by the U.S. Commerce Department to join
the transition converting from inch standards to metric standards
of measure or international System or Units (SI). An earlier study
found that one-half to two-thirds of U.S. exports are "measure
sensitive" causing potential foreign purchases to be placed
with countries using the metric units of measure. Since the metric
standards can be very involved, we will cover only the basics
to familiarize you with terminology and help in the conversion
from inch to metric. Currently throughout the world, many metric
standards are being used:
ANSI (American national Standards)
IFI (Industrial Fastener Institute)
DIN (German National Standards)
ISO (Int'l Organization of Standardization)
EC and CEN (European Economic Community)
Many of these metric standards have specifications
that are very similar to one another, but some dimensions are
not directly interchangeable. The availability of DIN standards
has influenced its popularity, but with the adoption of a unified
measuring system, ISO is becoming more and more popular, especially
with the introduction of ISO 9000.
To determine the diameter of a fastener, use
the above conversions then round to the nearest whole number.
#10 IS .190 in decimals multiplies by 25.4
millimeters = 4.826
4.826 can be rounded up to 5 which is called out as M5 diameter.
The length can be multiplies in the same way
to determine the length in millimeters.
3" multiplied by 25.4 = 76.20 millimeters
Round down to 76 which is called out as 76mm long.
Metric fasteners also have a course and fine
thread series although most fasteners are supplied in the course
series. The exceptions are hex head cap screws, socket cap screws
and hex nuts which are available in coarse and fine series. The
coarse metric has more threads per inch than a course threaded
inch standard fastener and therefore has a larger stress area.
Fine thread metric fasteners also have more threads per inch than
the fine threaded inch standard fasteners and an even greater
area of stress. To avoid stripped threads, it is recommended to
use a thicker nut more thread engagement and greater reliability.