I wanted to build a large LEGO helicopter with Technic frame and motor, so I designed this rotor blade fitted with a LEGO Technic pin. 4 of these blades go in a 4x4 round block with holes (part 6222) which makes it easy to put on a vertical axle. They don't fit very tightly but I could let it spin quite fast and they didn't budge. They do sag at the end however, but so do real rotor blades.