Rectangular. For aluminum ladders of all duty ratings and fiberglass ladders with side rails up to 3 in H x 1-3/16 in W. Also fits Articulated ladder in scaffold or stairway use. Mar-resistant rubber caps protect work surface. Fits aluminum series extension ladders with rails up to 3-5/16 in x 1-3/16 in , D716, D1100, D1200, D1300, D1500, D500 (20 ft to 24 ft ), M and M1 Multi-Master ladders. Includes paint can hook, mounting hardware and instructions.