Metric

How To Measure Thread Size Metric. Sewing thread size or count is a numerical expression used to indicate threads size, is the relationship between length and weight of yarn. To identify an inside thread (such as a filter ring on a lens), first take your best guess from age and origin to determine if its a metric thread then measure the diameter of the female (inside) thread.

Metric machine screw threads are defined by iso standards. To identify an inside thread (such as a filter ring on a lens), first take your best guess from age and origin to determine if its a metric thread then measure the diameter of the female (inside) thread. 2.thread sizes in metric are specified by diameter and pitch.