I designed these to hold central heating multi-skin tubes 50mm apart. Many radiators in Europe use the H connector to which you connect the tubes at 50mm center to center. I use the spacers to help me to keep the tubes in place while they are plastered in the walls. The clip can be used however for fixing any type of tubing: PVC, electrical cable, etc. I also put screw holes in the clips and if you cut them in half they serve as single fixation clips. The most common multiskin heating pipe diameters are 16, 20 and 26mm. I included those files.