K-4 (40mm flat profile / 45° with mitered corners or with full corners). Indoor single side aluminum snap frame, width of frame molding: 40 mm (front frame all around) , the overall depth of the light box is just 28mm. The aluminium frames simply snap open and close to allow fast and easy graphic change.Edge lit with T5 fluorescent tubes EC approved or SMD led lighting. Sizes A4, A3,A2,A1,A0 and custom sizes