Fitted a monoblock mixer tap for a customer today - she had bought it from B&Q. The connecting 'tails' - the tapered copper tubes that screw into the tap base & seal with an 'O' ring caused me no end of trouble.
Tried to trim one to length with a Kopex Pipeslice - deformed the tube badly. I though there was something wrong with the pipeslice & tried it on some 15mm copper pipe no problem.
On inspection, the wall thickness of the 'tail' looks about half that of normal copper tube. You could actually deform the tube with sufficient thumb pressure.
Chucked them in the bin & used some spare ones I had on the van.