These are four pieces of thicker acrylic measuring 24 inches by 11 inches so they fit on top of standard 20 gallon with about an inch in back for airlines. They have a protective clear coating to peel off as seen in the picture then will be very clear. Was once upon a time going to try and make acrylic tanks with these as I think it is the correct thickness or just use as tops for the tanks. Setting minimum bid at $8 for all four.