Very small rare earth magnets. These are 1/8" in diameter, and 1/16" thick. (Approx. 3mm x 1.5mm.) They're perfect for mounting aircraft ono flying stands; personally I glue one to the belly of each of my aircraft, and one to each flying stand, so they can be separated for easy storage and transport. (This also means you need much less stands than if you permanently glue aircraft to your flying stands.)