Difference between Metric and UNF threads

Metric (ISO) is the most widely used thread in industry and construction (except, of course, in burger-influenced countries...). For this ISO standard, there is the widest choice of accessories.

For the same diameter, the English ‘UNF’ pitch offers greater strength and more precise adjustment. This type of thread is traditionally used for sailboat rigging.

But the range, and the diversity of technical solutions, is more limited.


To compare the aspects of the 2 types of thread (with equal diameters):

Metric Pitch is easily measured with a calliper, 10mm = M10


However, reading the value of a UNF pitch on a calliper requires a conversion, so you can use this table as a guide: