Measuring for a replacement shade:
A. height of the shade.
B. width of the shade's top rim
C. width of the shade's widest point
D. width of the shade's fitter measurement across the bottom, which would fit inside of the holders base.
E. height of the fitter. Some are short necked, some are taller. This would be the measurement from the very bottom up to the beginning of the bulged section.