I set my default to 2. I use 3 -4 for quilting--that depends on the batting.

My Bernina is auto set at 2.25. I drop it down to 1.5 for paper piecing and up it to 3.0 for machine quilting.

i use 2.5 unless something different is called for.

What do these numbers on the machine mean? Is it in millimeters or in fractions of an inch? Do they all mean the same stitch length across all manufacturers?

I thought you were supposed to use the little ruler that came with the machine to measure how many stitches to the inch and go by that. 10-12 stitches to the inch is standard?

If I sewed at 2.5 on my Janome it would be maybe 8 stitches to the inch. Not many, in any case.

I think mine is auto set on 2.5. I use Carol Doak's paper when pp, so I don't lower my stitches. My good friend here on the board sent me the Carol Doak's paper. I LOVE it!

I set my Bernina at 2.5 for most piecing. If it is a pattern with a lot of seams I will set it a bit tighter, about 2.0, it helps hold those seams together, and if I am doing PPing, I will go a bit smaller .

For Quilting on my home machine I usually set it at 3. I like the look it gives the quilting.
peace

I use 2.5 for piecing.

I use 2.0 (default) on my babylock serenade for my piecing and 2.5 for binding.

Default stitch on my machine is 2.5 but I always bump it down to 2.

I have a Bernina the default is 2.5. That is what I use for piecing.