Package including:4pcs 2mm Hex Coupler, 8pcs M4 Screws, 2pcs 4mm Hex Wrench. Material：Made of brass. Durable and insulation, the brass material reduces vibration during high-speed operation, avoiding power loss or slipping. Inner Hole Locking: The motor shaft is securely fastened with an M4 screw (screws and hex key included). Outer Hexagonal Nesting: Directly inserted into the hexagonal slot of the wheel to ensure a seamless connection. A Bridge Between Motor and Wheel: It securely connects the motor shaft (with a 3mm bore) to the hexagonal hub (such as the wheel of an RC car), enabling efficient power transmission.