As the length of this page has gotten a bit long, I have moved discussion of the below listed fill-in stitches onto their own blog page. Clicking the name of any of the below fill-in stitches will take you to their blog page.
Thread used: Hardanger is normally worked in two weights of threads. For fabric with count of 22 through 25 I use size 8 and size 5 threads. Kloster blocks are worked in the heavier, thicker size thread which would be the size 5. Bar weaving, and fill-in stitches are worked in the lighter size 8 thread.
Within my blog pages I (since these are the threads weights that I normally use) will refer to the heavier weight thread as size 5 and the lighter thread as size 8.
Fill-in Stitches that I discuss are shown as hyperlinks below: