|Bamboo Clementina and four different needle packs|
For most of my sweater knits -- wool, cotton, bamboo,whether jerseys or double knit -- I've found that size 90/14 needle works well. The one exception was with the Tangerine Top. The fabric was Clementina, a bamboo rib. I used a size 80/12 twin needle for the hem, only because I've been unable to find twin ball points in size 90/14. (If you've got a source, please let me know.)
As I understand it, a stretch needle is generally used for knits made with lycra or elastic. It can also be used to sew a sweater knit. The stretch needle also has a ball point. The difference between a stretch needle and a regular ball point needle has to do with the size of the "scarf", the indentation on the shaft directly above the needle eye. (See Threads Magazine: Machine Needle Know-How.) My serger uses HA x 1SP needles, a type of stretch needle. This isn't the same as the standard ball point for a sewing machine.
So what happens if you mistakenly put the wrong needle in your serger? If you put the standard sewing machine ball point in, when it's the HA x 1 SP that's required? I did this just before my serger went "out of time" last year. The wrong needle may be what caused the problem. I don't know. Apparently "Miss Fairchild" had a similar issue. (Read this patternreview thread. It's not until the middle of page 4, that we learn its resolution.) So that I don't make that mistake again, I now write the word "serger" on the back of all my serger needle packages.
There is often brand and size info stamped onto the shank of the needle. But have you ever noticed that a light reflection often appears on the needle shank just where the pertinent size info is stamped? I've recently discovered it's easier reading this info by zooming in with the camera on my phone, rather than with a magnifying glass or (ha!) the naked eye.
Yes, size matters when it comes to sewing machine needles. And so does shape. Remember that many household sergers often require a special needle. Please be sure to choose the right needle for your project and your machine.
Helpful Sewing Machine Needle LinksOrgan Needle Co. - Product Information
Schmetz Needles - All About Needles
Threads Magazine - Machine Needle Know-How