Alvin 18" folding parallel ruler provides a fast, accurate method of drawing lines parallel to any reference line. Transparent blades for easy reading features non-skid pads on back to prevent slippage. Sturdy aluminum links provide the right amount of tension for drawing a line parallel to another line or reference point. Metal parts are non-magnetic and corrosion resistant. Opens to 3" spacing between blades. 18" length. Undercut and beveled blades are constructed from durable, clear plastic that will not warp or shrink.