Tri-Clamp sanitary fitting size is based on the tube outside diameter (OD). The flange diameter for each clamp size is as shown on the chart to the left for reference. Please note that the 1/2" and 3/4" sizes use the same clamp but different gasket sizes. This also holds true for 1" and 1-1/2" sizes. Feel free to contact us with any sizing questions prior to ordering.