I had the idea to tape a few magnets to my vacuum cleaner, one with a bagless pickup cylinder, in order to recover ferromagnetic materials I may have dropped (e.g. paper clips, screws, nuts, ball bearings, other machine parts) and failed to recover otherwise. They worked pretty well, but they automatically arrange (stack), which places the poles at the ends, and concentrates magnetic flux outside of the vacuum's canister. With this doodad, I can trap the magnets in place with the poles pointing inward, so the field should be stronger, and it should better trap our desired pieces. I curved the open side with the magnets to a 2" radius (4" diameter) so it should snug up to the surface of the canister.I printed in soft PLA (3 layers, .2mm height, 35% fill), which makes it easier to insert the magnets; they retain rather well, too. Initially, the idea is to just duct-tape it to the side of the cylinder. I might design a ratcheting strap at some point. 1/4" cube N50 strength magnets: http://smile.amazon.com/gp/product/B00GU1KGT8/ Vacuum cleaner similar to: http://smile.amazon.com/Dirt-Devil-Dynamite-Bagless-M084650RED/dp/B000F8EUFI