The Delta T Dishes have a number 1.5 thickness, German, Desag 263 glass coverslip bonded to the bottom of the dish for high N.A. applications and are also available with 0.5mm thick glass for low N.A. applications. They have an electrically conductive, optically transparent, ITO coating on the bottom surface of the dish that when connected to a Biotech's Delta T Controller heats the contents of the dish. Delta T dishes have 35mm O.D. and a 23mm central aperture.