This part is not so much Faulty as it is Out Of Spec. It can be used with a lot of fettling, just a pain to have to do it with a new part that should be otherwise easy to install.

For a few years now some replacement 4-inch hoses have been supplied in 100-mm diameter, being 1.6-mm or 1/16-in undersized. This makes them difficult to install on the nominal 4-inch diameter connector pipes. So it may require a bit of fettling with the screwdriver handle to stretch them out enough to fit. This picture from Mark Wellard in Australia shows an OEM 4" hose at top and a recent 100-mm aftermarket hose at bottom (although you likely cannot see the difference of diameter in the picture).

Grab a fat screwdriver handle (or any round stock or wood dowel). Insert the rod into the hose end parallel to the axis and side walls. Move the rod around the inside of the tube in orbital motion pressing gently on the ID near the end of the hose. This will press back any exposed burrs and slightly enlarge the opening by stretching the material a bit. Best if you can do this and test fit the hoses on the heater inlet pipe before fighting to get them installed at the radiator diaphragm connection ports.