1/2" Fitting = Designed to take 1/2" pipe, which has an Outside Diameter of 21.4mm
3/4" Fitting = Designed to take 3/4" pipe, which has an Outside Diameter of 26.7mm
1" Fitting = Designed to take 1" pipe, which has an Outside Diameter of 33.6mm
1 1/4" Fitting = Designed to take 1 1/4" pipe, which has an Outside Diameter of 42.2mm
1 1/2" Fitting = Designed to take 1 1/2" pipe, which has an Outside Diameter of 48.3mm
2" Fitting = Designed to take 2" pipe, which has an Outside Diameter of 60.3mm
2 1/2" Fitting = Designed to take 2 1/2" pipe, which has an Outside Diameter of 75mm
3" Fitting = Designed to take 3" pipe, which has an Outside Diameter of 90mm
4" Fitting = Designed to take 4" pipe, which has an Outside Diameter of 110mm