From the perspective of product structure and mechanics, the scheme of square shaft handle + transmission lock box is better than fork handle + transmission rod in general (especially when the transmission wheelbase is long). Therefore, the combination of square shaft handle and lock box is usually used for the external window of heat insulation profile structure. At the same time, we should pay attention to that. The length of fork handle should not exceed 50 mm. In the same way, most of the side hung doors adopt the configuration of square shaft handle + transmission lock box. Of course, thanks to the square shaft handle, it can well solve the demand of double-sided opening of the flat door.