Sturdy cable channel with clips. It is 20mm wide and 16mm tall, each module is 100mm long. Several can be connected in a row and paired with a bend and end piece.
Worked absolutely brilliantly, printed 20 of these in one go on my P1P to use in the electronics enclosure on another printer build. It all came out flawlessly, and will be using this on all my builds from now on as I can make it all exactly how I want, and much cheaper than having to buy instead.