With all the wild fires and smoke this year I wanted an air filter for the house and I did not want to buy an expensive device that uses even more expensive filters. I designed these clips for my inexpensive 20 inch Lasko box fan. The clips will hold any 20" x 20" x 1" furnace filter. I used a reusable and washable filter I found at Lowes but any 20x20x1 filter will fit. I designed two sizes of clips. The large clips do hold quite well and would make for a strong permanent installation. The small clips tend to sag and slide a bit, but do work just fine. The small clips are easier to install as they are more flexible. If I had a garage I would use this while woodworking to keep the air clean. The small filter clips can be printed with no support, the large clips need support for the small overhang that slots into grill on the fan. Print the clips and snap onto the fan slotting the front of clip into the fan first and then pulling over the back of the fan. Be sure to put the beveled edges up so the filter will slide in and out easily. Any 20x20x1 inch furnace filter will fit.