Abstract: A flight unit in which a flight is connected to a shaft rotatably and without possible wobbling and a dart comprising the flight unit are provided. The flight unit 2 is a part of a dart comprising a shaft 30 and a flight 40. The shaft 30 comprises a shaft body 31, a protrusion 32 provided at one end of the shaft body 31, and a flight connector 34 provided at the tip of the protrusion 32. The flight 40 comprises a hollow cylinder 42 in which the protrusion 32 is slidably fitted, vines 41 at the bases of which the hollow cylinder 42 is provided, and an open cavity 43 adjoining the hollow cylinder 42 and in which the flight connector 34 is slidably fitted. The open cavity 43 is provided to the vines 41 and comprises no exterior walls.

Abstract: An automatic opening and closing system for opening and closing a window by automatically locking and unlocking a lock section of the window and by using a sensor, with a lock locking and unlocking mechanism for locking and unlocking a window of a building Apprising a stand fitted into a hole opened in one window frame, a lock section constituted by a lock body provided at this stand, a lock piece engaging with the lock section provided at the remaining frame, and a first controller for moving the lock piece, with the lock locking and unlocking mechanism actuated by operation of the first controller so as to lock and unlock the window, and the window opening and closing mechanism for opening and/or closing the window comprising a fitting lug body fitted to the frame, a stopping lug provided at the fitting lug body, a drive section such as a motor etc.