Can you use the double needle on any machine? Or does it have to have that feature? I have a Janome QSA and I don't see how I could do it. How would I thread it?

mine has two places for thread

You need two thread holders as well as a throat plate that has an opening wide enough to accomodate 2 needles moving up and down.

Any machine with a single needle hole in the plate cannot use a double needle.
If you machine has a zigzag stitch, it should be able to accomodate a double needle. Please note the should. Not all actually can. Check in your manual.

Any machine that does a zig zag stitch and has a foot with a big enough hole to accomadate two needles should work. If you only have one thread pin you could set up another spool of thread on a stand behind the machine take the plastic lid off of a small butter tub etc. poke two holes in it. One to put your machine's spool pin through and the other to thread the additional thread through. The tricky part is threading both threads through your machine. You can do great things with a double needle. I have a very good serger but I was not interested in the "chain stitch" that I could have gotten for more money. I can imitate the same stitch with my regular machine and a double needle. The big difference is that I don't have to worry about pulling a thread and having the whole thing unravel. I am sure you have had that happen on a knit garmet with a chain stitch hem. It also allows you to do beautiful pintucks which are very decorative.

I would be interested in knowing how to do this since I have several machines that will take a double needle and never used the feature. :-D

There's nothing in the manual about double needles. I will ask at the LQS where I bought it though. They're very good about showing me "stuff"! Thanks for the info.

I used them in my old machine, I just made sure to buy the ones that will easily fit in through the opening in the plate. They come with different spaces between the needles :wink:
My new machine has a setting for them :D:D:D

I noticed the differences when I first checked them out. Wondered what that was about. I also checked the price out! Let's just say that I won't be getting one today or tomorrow (if they will work on my machine)! I do have two spindle holders on my machine and my DS (dear is this case) made a cone holder for me too.