Choke area is shorter. 2-3 inches vs 6 inches. Most screw in chokes are turned. This leaves small ridges to collect plastic. It is easier to lap a longer choke to smooth it. Inlet area(back of choke) is usually 10-15 thou over bore. This prevents wad/shot catching due to variances in bore/choke. Wad goes into big area, expands then gets choked. Varies from brand to brand. I've had good luck with Seminoles and Optima chokes.