WHAT IS IT?
Overcasting is handsewing stitches over the edge of the fabric. It’s a very simple hand sewn stitch, consisting of slanting stitches wrapping around the raw edge. Some sewing machines have an overcast stitch function, as well, that looks similar.
Overcasting on seam allowance
WHEN DO YOU USE IT?
Overcast to finish seam allowances or raw edges by hand and to stop the fabric from fraying. Compared to other methods, this is a slow seam finish, but it can come in handy when you want to finish seams that are hard to get to by machine. If you’ve forgotten to finish a seam allowance, it’s easy to go back in later on and overcast the edges by hand.
HOW TO OVERCAST
Thread a handsewing needle with single thread. Starting at one end of the fabric edge, go up from the wrong side and place the needle above the starting point, coming back up from the wrong side.
Repeat along the edge of the fabric, placing the stitches close enough to keep the fabric from fraying, about ¼” (6mm) apart. Don’t pull the stitches too tightly; leave them loosely wrapped around the edge.
Source : The Sewtionary An A to Z Guide to 101 Sewing Techniques + Definitions
About the Author : Tasia ST. Germaine