A common way to make a shank is to use a tooth pick or something like it to hold your button away from your fabric while you stitch it in place. This doesn't work very well for me because the toothpick always seems to move away while I'm trying to hold it in place and stitch at the same time. Using a straight pin underneath does not usually give me enough height for a shank. Today I discovered that if I use the thick end of a sewing machine needle under my button with the sharp end secured into the fabric just beyond the button, I get the perfect sized shank and the needle does not move away underneath until I remove it. This method worked very well on my knit twinset.