On Mon, 8 Apr 2013 13:42:51 +0000 (UTC), David Scheidt wrote:
Assuming your talking about spun poly thread, and not something like
'wooly nylon', serger thread is just thread. Small diameter thread, of
course, but still, just thread. It works just fine in most machines
(apparently some can't tension small threads well, but I suspect
that's user error.).

Most of the common serger thread in the US is Maxilock, which is loosely
twisted spun poly Tex 27, and often lumpier than standard sewing machine
thread. I have an accidental comparison photo here, third photo from the
bottom: http://www.picturetrail.com/sfx/album/view/22801244 The neon
green in the bobbin is Maxilock serger thread, which I wanted for high
visibility. The black in the needle is Gutermann Mara 100, tex 30, and my
usual thread these days. The light blue escaping from the accessory box
is the standard consumer "sew all" Gutermann polyester, tex 30.

I'll use Mara 100 on my sergers, but it's very rare that I'd consider
putting Maxilock on a sewing machine -- I can tell the difference between
stitch evenness. And yes, I do know how to tension a sewing machine correctly,
and match needle size to thread diameter.

(Mara 120, btw, is tex 25, and is also nice thread for light fabrics).

Kay