>From the Thordarson Catalog: Chokes, Universal Swinging and Smoothing T-20C51 5/25 MA 15/35 Hy T-20C53 60/100 MA 8/17 Hy T-20C64 100/150 MA 3/7 Hy T-20C55 150/300 MA 2/9 Hy T-20C49 200/250 MA 4/5 Hy T-20C56 250/375 MA 4/8 Hy