These are high quality and low resin 100% carbon fiber weave propellers. The stiff carbon construction gives durability as well as an increase in overall motor efficiency. The dual mountings mean these will fit on most multi-rotor motors. You can use the standard mounting with the 4mm shaft (ream for larger shafts) or use a tightening cover with 12mm centers and M3 bolts. High Carbon Content - High carbon density of these propellers offer extra rigidity, lower weight, and greater durability than many others available. Carbon Fiber 15x5.5 Inch Propellers Specifications: Length: 15 Inch Pitch: 5.5 Inch Weight: 20g (Each) Shaft Diameter: 4mm Cover Plate Hole Centers: 12mm Hub Thickness: 3mm Rotation: CW and CCW Package Contents: 2x CW Carbon Fiber 15x5.5 Inch Propellers 2x CCW Carbon Fiber 15x5.5 Inch Propellers