I-beam levels aluminum top read 3 vials: 1 level/2 plumb length 24 inches. Rugged extruded aluminum frame, black anodized for long life and shock-protecting plastic end-caps. Vials fit into precision-stamped cutouts and are held in place by Quick-Change ABS plastic vial covers with screwed-in clear acrylic lenses for easy access and replacement. Level vial features large top-read window.