A sewing thread has to have an excellent level of linear density regularity along its length. There can be no room for thick and thin places or twist variation. The gold standard for evenness testing is still the Uster tester although some competitors have entered the market with varying degrees of success. In the Uster tester the thread is run through two conductive plates and thus becomes the dielectric material. Any variation in the mass of the thread will therefore cause a variation in the capacitance and the variations can be instantly and continually captured and digitally recorded by computer. The most commonly used value for thread evenness is CV% (coefficient of variation) and the tester also provides recorded traces and graphs of the variation which are excellent for quality control and process control.
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