US Patent 8668049 Ladder

A ladder comprises two stiles and at least a step unit mounted between the two stiles. The step unit includes a hollow step, an inner sleeve and an outer sleeve. The inner sleeve is fit into the hollow step, at an end of which a position restriction portion is located to prevent the inner sleeve from moving out, and the outer sleeve is adapted to surround the end of the hollow step. Besides, a fastener is set, the fastening end of which is passed through the stile, the outer sleeve and fastened in the inner sleeve. The present technique solution has a high supporting strength and a high shear resistance.