Will not discolor or warp with age and handling. The machined finish and hand-polished edges of the C Series (clear) and F Series (fluorescent) meet or exceed government specifications. The F Series is extremely popular because the refracted light has an illuminating effect on the drawing by accentuating the triangles edge. All models feature a double-taper cutout center for quick, easy lifting from any angle. Supplied in poly bag with hanging hole.