Its designed for indoor or outdoor use. The contoured supports are 3/8 x 4 inch rolled steel that is formed to shape a smooth comfortable seat and backrest. The steel leg consists of a 2 1/2 inch square support tube welded to an arched 3/8 x 4 inch formed steel base. The entire frame is coated black for long life and good appearance. This frame is specifically designed so it can be fitted with your choice of 2 x 4 inch pressure treated No. 1 Southern Yellow Pine, 3 x 4 inch "C" and better Douglas Fir, or 4 x 4 inch gray, cedar, or brown Recycled Plastic slats. Comes standard with Surface Mount legs.