581-18 Style: Len.:18", No. of Vials:3 (part# 581-18) This item features: -Solid I-beam frame with magnetic edge. -Top read window. -Replaceable acrylic vials. -Beveled end plates protect from shock. -High visibility yellow. -Vial Positions: 1 45 , 1 Level, 1 Plumb. -Vial Material: Plastic. -Base Type: Magnetic. -Structure: I-Beam. -Brand Name: Magnetic Unitek . -Type: Builders Spirit Level. -Price is for 1 Each.