falling-off prevention device (1) comprises a coil spring portion (2), a cylindrical body (3). The coil spring portion (2) has a coil spring body which coil wire is wound in substantially the same diameter (2A). One end of the coil wire that extends from one end of the coil wire of the coil spring body (2A) (2B) is located in a concentric circle arc-shaped coil spring body (2A) than larger radius in the radius of the coil spring body (2A). The coil spring portion along the center axis of the coil spring body (2A) and the other end side coil wire extending from the other end of the coil wire (2C) in the position outside of the coil spring body (2A) of the coil spring body (2A) It is bent toward the one end side of the coil wire of the main body (2A). Inside the cylindrical body (3), the coil spring body housing space spring body (2A) is accommodated coaxially (4) is formed. The tubular body (3) has a coil spring body accommodating space (4) and formed coaxially a screw portion (5).
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