When you use invisible thread, what do you adjust the tension to? Ok, nobody laugh at me now, are the two numbers on the machine, as in 2.5 3.4 the tension numbers. Is the first bottom tension and the second the top.

Ok, I think I heard a snicker out there ;)

Your bobbin tension is adjusted by turning a screw in the bobbin case :wink:

I would think those are the stitch lenth and width numbers
what kind of machine do youhave?

Have you tried without adjusting anything? I'd try that first.

Hard to say what the numbers you mention mean without a point of context.

I would buy a second bobbin if you are going to change your bobbin tension.

No snickering here! I had problems with it too.

I found I could use the tension just as it was when I sew with polyester threads and used the polyester in the bobbin as always.

I use YLI invisible thread in all my quilts & never touch or change the tension. I have a Viking Rose vachine.

i think the numbers you are asking about are your stitch length/width numbers, if your machine tension dial has numbers on it they are just 0,1,2 ect...it is a round dial usually close to the take up; you run your thread around it...make sense?

On my machine, the upper tension knob is numbered 0 to 10. When using invisible thread on top, it helps to reduce the upper tension because of the stretchiness of the thread. I reduce my upper tension by 2 or 3 numbers.

Many people do not use invisible thread in the bobbon. If you do, be sure to use a metal bobbin, do not overfill the bobbin, and do not wind the bobbin at top speed. Because of the stretchiness of the thread, it can distort a plastic bobbin and get stretched as it is wound. When I use invisible thread in the bobbin, I do not adjust the bobbin tension. As other people have noted, bobbin tension is adjusted by means of a tiny screw on the bobbin; adjusting this screw is fine as long as you know what you are doing, but should not be attempted if you have not read and understood a detailed explanation of safeguards you should take.

I agree that the 3.5 type numbers you are describing probably belong to the stitch length and stitch width knobs. Change one to an extreme and manualy turn the wheel to see what happens. (Manually turning the wheel ensures you won't break a neede if you happen to adjust it to a zigzag while having a straight stitch foot on your machine.)