Have questions about sewing machine needles? Here's pretty much everything I know:
The needle "system" is the "size" your machine uses. It is based on the overall length, the shank length, diameter, etc. Our Mini Brute machine uses System 135 x 17, as does the Singer 111W and Consew 206RB. A Singer 107, however, uses System 135 x 7, and the Consew 272 uses a System 134. There are many more "system" sizes.
Most, if not all, "industrial" or commercial machines use needles with a round shank.
Most home machines use System 130/705H. These have a flat side to the shank.
After you determine your system, the next "size" depends on the size thread you are using. This numbering system is usually expressed in 2 numbers, such as 120/19. The first number, 120 in this example, is the metric size. The second number, 19, is the number originated by Singer, sometimes referred to as the US size.
The hole the needle punches in the fabric needs to be big enough for the thread to go through. It should also be small enough so that the needles hole does not leak or weaken the fabric.
So, for thread size V-46, use needle size: 90/14 or 100/16.
For thread size V-69, use needle size: 100/16, 110/18 or 120/19.
For thread size V-92, use needle size: 120/19, 125/20 or 130/21.
For thread size V-138, use needle size: 125/20, 130/21, 140/22 or 180/24.
We sell System 135 x 17 (as that is the system our Mini Brute uses) in sizes 100/16, 110/18, 125/20, 140/22 and 180/24. We also sell System 130/705H since many of our customers sew with a home machine. We carry it in size 120/19. Smaller sizes can be purchased at local sewing or hobby stores.
Sewing with PTFE thread, such as Tenara, may be improved by using MR needles. These needles have a unique shape, deeper grooves and smaller diameter. They are advertised to be stronger than conventional needles and skipping stitches is reduced. We sell these in size MR5 which is similar to conventional needle sizes 120/19-130/21.