3003 Aluminum Diamond Plate

Aluminum diamond plate, also known as checker plate, is a type of light-weight metal stock with a regular pattern of raised diamonds or lines, although modern manufacturers also make a raised and pressed diamond design. Used on stairs and catwalks in industrial settings, the added texture reduces the risk of slipping. Diamond plate is also used on the interior of ambulances and on the sides of firetrucks. Diamond plate can also be used decoratively.
The term tread plate can also refer to diamond plate, but it could also be other anti-slip textures.

It provides maximum skid resistance regardless of how the plate is laid or the angle from which it is approached. Patterns are continuous whether adjoining plates are laid end to end, side to side, or side to end. Cutting waste is reduced to a minimum. Cleaning is easily accomplished with a hose, brush, or mop, with rapid and complete drainage

3003 aluminum is the most widely used of all aluminum alloys.  It is essentially commercially pure aluminum with the addition of manganese, which increases the strength some 20% over 1100.  Thus, it has all the excellent characteristics of 1100 with higher strength.It has excellent corrosion resistance and workability, and it may be deep drawn or spun, welded, or brazed.  This alloy is non-heat treatable.

Reference:
Earle M. Jorgensen Company - Reference Book