text: Well, the shotgun gauge bore diameter are\n10 gauge  0.76" (19.7 mm) \n12 gauge 0.73" (18.5 mm) \n16 gauge  0.66" (16.8 mm) \n20 gauge  0.62" (15.6 mm) \n28 gauge 0.55" (14.0 mm) \n\nThe hull thicknesses very from manuafcturer to manufacturer, but are larger than the bore diameter. hope this helps.