Hi Paul, The holders are as you have deduced, made of plastic pipe or ducting which in this instance are 54 mm outside diameter. The crucial measurement is the thickness of the pipe wall. The thickness I used was 1.5mm which means that the slit opens widely very easily (I was fumbling a bit in the movie clip, but that was just me being clumsy and not a difficulty opening the slit in the pipe). I tried using thicker plastic pipe and found that anything above about 2mm was too inflexible. All the tube is doing is supporting the 2 metre long roll and as long as the pipe opens easily along the slit there is no problem.