These are 55mm (2.2inch) Blade Propeller Propeller for 6x15mm, 7x20mm 8.5x20mm Coreless Motor DIY Micro Quadcopter. The propellers with 0.95mm mounting hole can be firmly mounted onto 1mm 4-axial motors. Their smooth surface can greatly decrease the wind resistance during the flight. Therefore, thePropellers can rotate in high-speed easily when reliably mounted on the quadcopter. Besides, the propellers are made of high-tenacity material and thus can sustain crashes. You can have these 4 propellers, or let’s say 2 pairs (red and black) for your mini-copter just to take off, or hold them as spare parts for replacement.