Now that we know what all those numbers mean, what does that mean from a practical perspective when we are trying to choose what size needle to use? Although our needles are standardized, our thread is not. 

Currently, thread is measured in three different systems. The system used for cotton has been a ‘fixed weight’ system, meaning that length of cotton yarn weighs a certain amount. In addition, cotton thread is manufactured in 2 and 3-ply threads. Thus you will
see a designation of ‘50/3’ or ‘60/2’ on a spool of cotton thread. The first number is the  ‘weight’; the second is the number of plies. A 50/3 thread will be heavier than a 50/2 thread. In a fixed weight system, the higher the number, the finer the yarn. A 30 weight 2 ply thread is thicker than a 60 weight 2 ply thread.

This system was applied somewhat erroneously to polyester threads when they were first developed. It was meant to provide a frame of reference that the home sewer could use to tell what size thread they were buying in relation to the cotton thread they had used in the past.

There is also a fixed-length system, which is generally applied to continuous filament threads, such as silk thread. It means that a fixed weight of a fiber will equal a variable length of fiber. Higher denier threads are thicker, lower are thinner. 

The only reliable method for measuring thickness of thread is the TEX system, but at this point it is not used widely in thread marketed to the home sewer. The TEX system is a standardized system of measuring the diameter of the yarn and can be certified by a laboratory.

Most companies rely on a ‘weight’ measurement, and what one company calls a certain weight will not be the same as the same weight from another company, even when number of plies or ‘count’ is added. The various measuring systems are so obscure and difficult to understand to the layperson that often the ‘TEX’ of a thread is assumed to be the ‘weight’.

Okay, so what do we do? If you use a thread frequently, you probably know what needle works best for it. Here are some hints for matching needle to thread size:

Thread a machine needle onto a length of thread. Hold the thread out in front of you horizontally. Tilt one end to a 45-degree angle. If the needle slides easily down the thread, you are close. If the needle won’t move, try a larger needle. If the needle just flies down the thread, try a smaller one.

If your needle is larger than it needs to be, you’re not only inflicting more abuse on your fabric than necessary, but you are actually causing more wear on the thread. The more extra room the thread has to flop around in the eye, the hard it is on the thread.

We honestly do not recommend this just so we can sell more needles! A needle that has been used for 8 hours of actual stitching has penetrated fabric many thousands of times, depending on how fast you are running your machine. The tiny tip of that needle eventually wears out, even on the best quality needle. A dull needle damages fabric and causes skipped stitches, broken thread, and lots of frustration.  WHEN IN DOUBT, SWAP IT OUT!