using a overhand knot in each stitch,works well if you are sewing thin leather or if you are sewing multiple layers of leather and drill the holes instead of using a diamond shaped awl to get your saddle stitch slant. I always thought that (overcasting) is when you center the thread to star,t and then bring one end of the thread over the top to the opposite side also do the other thread,and continue as you normally would. Please correct me if I am wrong on this. Good luck