The tex size is a measurement of the gram weight of 1000 meters of greige or un-dyed or finished thread. Examples include: T-18 – T-27 for light weight sewing; T-30 – T-50 for medium weight sewing, etc.
The metric size is the most common system used in Europe and is the number of 1000 meter hanks per kilogram (or number of 496 yd hanks per lb.). Examples include: M180 – M120 for light weight sewing, etc.
The yarn size is a measurement used for the number of 840yd hanks per pound and is many times also referred to as the spun size. The yarn size generally includes both the yarn size and number of ply. Examples include: 46/2 representing 46’s cotton count – 2 ply.
The average single-end break or SEB is measured in pounds and is only for comparative purposes and should not be used for minimum strength requirements.
In Hong Kong, a common ticket system used for spun polyester is using the yarn size but dropping the “/”. Therefore, a 50/2 yarn size is called a 502, a 60/3 yarn size is called a 603, etc.