T12 tubes are fluorescent tubes with a G13 socket but have a diameter of at least 38mm. This is 10mm wider compared to the popular T8 tube, that has the same socket. T12 tubes are not very commonly used anymore, because they are not energy efficient. But the advantage of a T12 is that is has a short start-up time. Flickering of this tube is less compared to normal G13 tubes. Please check the dimensions before placing your order.