Abstract: A device for locking a corner post of a loading platform, or flat, in its vertical operative position, including a pin at the lower end of the post accommodated by a socket fixed with respect to the platform, and a torsion spring which is stressed during the vertical downward movement of the post when the post is erected. A hook-shaped catch on the post engages a plate fixed with respect to the platform to prevent accidental movement of the post from its operative position. A lever, arranged at an angle to the corner post, interconnects the corner post and the torsion spring. The torsion spring is also stressed when the corner post is folded down upon the platform in its collapsed condition.