Plastic sealing cap, 2 1/2"
The inch specifications of the pipe diameters (outside diameter) are not to be equated with the inch (25.4 mm).
In the past, the dimensions used to refer to the inside diameter of the tubes and the outside diameters were correspondingly larger (approx. 33 mm for 1 inch). Over the decades, new production processes and better steel qualities have made it possible to produce thinner-walled tubes. As tools (taps, etc.) and accessories were already available for the "old", larger outside diameters, the outside diameter was retained and the inside diameter of the tubes was increased.
That is why "inch" tube dimensions are now defined metrically. Please inform yourself before buying which clamp / pipe connector fits your needs.
Please refer to the following table:
Tube size in inch = outside diameter in mm
Tube 1/2" = Ø 21.3 mm
Tube 3/4" = Ø 26.9 mm
Tube 1" = Ø 33.7 mm
Tube 1 1/4" = Ø 42.4 mm
Tube 1 1/2" = Ø 48.3 mm
Tube 2" = Ø 60.3 mm
Tube 2 1/2" = Ø 76.1 mm
Tube 3" = Ø 88.9 mm