Sola Big"X" Box 16" Aluminum Level w/Contoured Grip - BX16 Rugged 6063 Aluminum Alloy for the highest accuracy for perfect measuring results. Accuracy  .5mm/M in standard position,  .75mm/M inverted Shockproof acrylic block-vials. Sonic welded not glued. Vials will neither crack nor break when used at the jobsite Shock absorbing ends allow level to withstand rugged use Easy to read vials: 30% larger vial bubbles reduce reading errors Lifetime guarantee against leakage and fading of vial: In proper use of the level, vials will neither leak nor fade in the sun