 Browline glasses are constructed in such a way that the upper portion of the frame is thicker than the lower portion, simulating additional eyebrows or otherwise drawing attention to the wearer's natural brow line.The most common means of construction is for the upper portion of the frame (the "brows" or "caps") and temples to be made of plastic, with the remainder of the frame (the bridge and eyewires, or "chassis") to be made of metal.The chassis inserts into the brows and is held in place by way of a series of screws.