I place one of these in between a fan and whatever surface it is mounted to. The small washers (not shown in photo) are optional under the screw head, it helps the fan lightly "float" in between the screw head and the mount surface. I use just enough tightness so the fan holds in place. I tend to sandwich the fan between an intake duct and a fan duct, so two of the squares are needed for my designs.

The material here is 1/16" thick or ~2mm thick adhesive backed craft foam from a craft store. I like adhesive as it holds it in place, but it's not required. I cut the adhesive version adhesive side up. I have kerf compensation built into the drawing, assuming a 0.2mm laser kerf.

If you look closely, you'll see these on my fan ducts on my other designs.