R39 Glass Lamps, Base Size Comparisons

All of the above lamps have R39 glass.
The three bases are E12, E14 and E17 from left to right.

Many lava lamps and furniture lamp fixtures state a wattage, commonly 25W, and a R39 or R12 glass size but do not state the base size. Not everyone has a caliper tool to measure the base diameter. If you have a caliper tool then refer to the diameters below. If you do not have a caliper tool then, to calculate the base size of your original lamp, wrap a piece of paper around the outside of the threads, and mark the paper and you have marked the circumference. Lay the paper out and measure the marked distance that will tell you the circumference.

If the circumference is about 1-7/16” then the base is E12. You can order the 25W E12 lamp here. You can order the 40W E12 lamp here.

If the circumference is about 1-11/16” then the base is E14. You can order the 25W E14 lamp here.

If the circumference is about 2” then the base is E17. You can order the 25W E17 lamp here. You can order the 30W E17 lamp here.

This is how the above sizes are calculated:

E12
The base diameter, outside of the threads, is about 11.6mm, times Pi equals 36.43mm which equals 1.43” circumference.

E14
The base diameter, outside of the threads, is about 13.63mm, times Pi equals 42.8mm which equals 1.68” circumference.

E17
The base diameter, outside of the threads, is about 16.37mm, times Pi equals 51.4mm which equals 2.02” circumference.

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