Basically, its a loose 2-thread flatlock that has been turned inside out.
So, to do a flatlock, you have to convince your needle that its really an upper looper.
Settings: Left hand needle only. Stitch selector "A" (because of the left needle). Length: standard 4. Width: 7.5mm
Thread the lower looper as normal. Then place the needle thread into the upper looper path and go ahead and jet it through. Now, this is the tricky part. There are three things that line up when you lock your loopers to jet the air through. You need to pull the thread out just before the upper looper tube. Unlock the loopers and grab that thread at that point. Pull it up and hook (there's a hook on the front of these machines for this), then thread the needle as if its a needle thread (up and over the "e" and through the left hand needle).
Now, if you have never set up a flatlock before, this is the really weird part. You need to engage your subsidiary looper. There is a little metal spring on the top of your upper looper and a black piece of metal attached to that. Push the black piece to the left and back a bit until you hear and feel it click into place. MAKE SURE THAT YOUR LOWER LOOPER THREAD IS NOT CAUGHT INBETWEEN ANYWHERE!
Serge over the top of the fabric, with Sulky Solvy or other water soluable stabilizer on the top of the fabric.
When done, pull the stabilizer to the edge of the fabric. This will turn the stitches and make the blanket edging. You can rip off the stabilizer or just get it wet and it will dissolve.
For other sergers, if you can do a 2-thread flatlock, you can do this stitch, but you need to adjust your tensions rather than threading it weird. And you need to serge off the edge of the fabric to give the stitch room to turn.
For Suzanne's hoodie, we used woolly nylon to give it a thicker look. You can also run crochet cotton through the Imagines/Evolves to give it even a thicker stitch yet.
Military wife of a deployed soldier. 
amazing 
thanks!
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