Lipped 4 1/2" dia. The 8-9 day vegetable wax sanctuary lights are designed to be burned in a sanctuary glass at an ambient temperature of approximately 10+degrees and in this way will last the time indicated. When the temperature is below this level the flame is unable to generate enough radiant heat to melt the vegetable wax and provide sufficient fuel to continue the burning process. This also leaves wax residue on the side of the container. The way to raise the temperature inside the glass is to fit this heat retention cap in the autumn and remove it in the spring. Leaving it on during the summer may result in the candle melting more fuel than it needs and drowning the wick.