There are three basic mounting rail variations: 35mm x 15mm, 35mm x 7.5mm, and asymmetrical. The 35mm x 15mm symmetrical rails are deep enough to readily accommodate mounting hardware. The 35mm x 7.5mm symmetrical rails are lighter in weight and are often spot welded in place rather than installed with hardware. Asymmetrical rails provide greater structural strength and they ensure the directional alignment of the blocks which eliminates installation errors. Rails are steel, zinc chromate plated, and are supplied in pre-slotted 1.0 meter lengths. Rails are also available unslotted and cut to various lengths.