Another way is to pick up one of these stiching brustes and use Paths.
Paths are perfect for this kind of thing, use the pen tool to draw out your stitching line, then add a stroke with brush.
This will create a perfect line of stitching off any size u want with any brush you want depending on your brush settings at the time in the right direction. The pen tool isnt easy to get use to so practise a bit in its uses and its various functions but you'll get the hang of it
Theres a lot of tutorials that need paths on this site, im sure you will find a few but heres one that I found quite helpful:
BioRUST.com :: Tutorials >> Abstract Wireframes
good luck!