Shatterproof 4mm HD glass is supported by a 9mm MDF backboard (most others just 3mm ), surrounded by a 1/17″ gap with the scalloped corner design to give a seamless finish. Shape Scalloped. Size 22×30, 24×36, 30×40 22×30/24×36/24×32,/24×40/26×38 22×30/24×36/24×32,/24×40/26×38 22×30, 24×36.