In the armrest design of office chairs and gaming chairs, the flat tube armrest is equipped with a 1D adjustable function. The flat tube design is different from the traditional round tube, and the appearance is more simple and smooth, in line with modern aesthetics, and full of lines. Although the 1D adjustable function seems simple, it is very practical. It can easily adjust the height up and down to meet the needs of users of different heights for the armrest height. When used for a long time, it can be flexibly adjusted according to the sitting posture, so that the arm can find a comfortable support point, effectively reducing arm fatigue.