A field emission element includes an elongated solid body, a carbon nanotube yarn and an electrically conductive adhesive agent. The arrow rest possesses several slits extending from the aperture so that when the arrow is shot, the aperture may distend to accommodate distortions of the arrow shaft and to allow the arrow vanes to pass substantially freely therethrough. The two holding bars are parallel to each other, and the two holding bars of each of the holding units are rotatably assembled with the two holding bars of a next one of the holding units to rotatably assemble all of the holding units one by one and form assemble apertures between adjacent ones of the holding board.