Anchor coton a Broder 30
Coton a Broder is one of my favourite threads to work with. It has a really tight twist which is perfect for practicing all sorts of stitching - especially good for knotted stitches. It is not strandable - just use it as it is; you will never want to stitch with any other thread after using it.
It comes in handy hanks, too. Take the bands off, open up the hank and cut through at the knot - perfect lengths for stitching! Thread the spare lengths through the band (the one with the shade number) to keep them tidy.
This is finer then the No. 16 and 25, which are also available.