Metric number

Metric number (abbreviated Nm), also known as metric numbering.

For sewing thread: indicates the ratio of length in metres to mass in grams. For example, 40 Nm means that 40 metres of thread have a mass of 1 gram, while 100 Nm means that 100 metres of thread have a mass of 1 gram. The finer the thread, the higher the numerical value. Used as a specification for sewing threads.

For sewing needles: indicates the diameter of the needle in 1/100 mm above the hollow.
Fine needles: Nm 60, Nm70
Medium needles: Nm 80, Nm90
Thick needles: Nm100, Nm 110, Nm 120