Size: Diameter: 444.5mm / 17.5", Fits 18-20 inch Lampshade Openings(Please confirm the inner diameter of the lampshade before purchase).Advantage: Made of 1/8 inch (2.7mm) thick DOUBLE SIDED double smooth white acrylic sheet with a 3/8" (10mm) center hole. this diffuser is thicker than other diffuser and can withstand the heat generated by the lamp. It has good light transmittance, durability, heat resistance, and long service life.Application: This diffuser can soften and diffuse the light of the bulb, is great for eliminating glare from CFL or LED bulbs, and improves visual comfort by reducing eyestrain, creating more comfortable, eye-friendly lighting. You can also use it to direct light downward for accent or improved reading light.