No, the pipe is all 1 1/4″. The valve casting itself is actually shorter, so the feet of the radiator are jammed into the floor. For example if you replace legs on a chair
with shorter legs, your chin will hit the table, even though
the legs are the same thickness.
And if we add a coupling to extend the feed pipe the radiator will be too high and it will float in the air.
This problem must happen all the time….