10 gauge (slightly thicker than 1/8" - the same thickness as the frame rails) steel. Price is for one complete frame (four pieces). Also available individually.
Designed to box 1935-1940 Ford frames from ahead of the front crossmember to behind the rear crossmember. Four plates, to box one frame. The plates are divided into front and rear sections to make it easier (and cheaper) to ship and easier to handle.
The plates were designed to fit the frame rails corner to corner.