This technique is another nice way to tack up a hem. It can be applied to the cuffs, neck or hemline of a sweater. It involves two simple movements that are illustrated below.
Draw the threaded yarn through the right half of a stitch on the folded up hem from right to left. Make sure it passes underneath the working yarn on the way out.
Next insert the needle through a purl bump on the backside of the fabric you are tacking the hem to. Pass the needle from top to bottom. If you are sewing a straight seam, make sure that you are sewing through purl bumps that are along the same row. Otherwise your hem will be uneven.