Servings come in more than one thickness; but .021 is pretty common. It really depends on where you want to end up. Electrical tape will leave a residue. You could serve over the serving with upholstery thread, or floss-you could carefully crimp the nocks but none of these methods are perfect. A thicker serving is .026, and that may be the solution. What is best is to reserve the string and add string material to till your nock fit is exactly what you want. lay strands parallel to your bowstring and serve over that-test with your nock till you get it right. There may be a tutorial somewhere on this site.