The light fixture says "40W Type B Only" and I know type B is candleabra but the candleabra shape ones don't fit as there is a strut holding a Tiffany style shade over the top of fixture. The bulb on the right is what came out of the fixture.

(I'm referring to the one on the right. The A19 on left is for scale) Edit: Also the bulb size matters on this fixture. The bulb is 2-1/4" tall from the bottom of the base and the glass bulb diameter appears to be 1-1/4"

2 light bulbs of different sizes

  • Candelabra would be my first guess, not having measured it.
    – keshlam
    Dec 18, 2023 at 23:44

4 Answers 4


That looks like a G40 bulb with an E17 'intermediate' base. To confirm, here are the measurements of one with an intermediate base:

G40 bulb is

If the base size is correct but the top size is not, you can look for similar bulbs such as a G30. G indicates a 'globe' shape and the number is a dimensional measurement. There is some variation in size of the globe size between manufacturers even with the same G measurement. You may note the bulb also says GB40W on it, which is a hint.

There are also LED replacements available for this bulb style.

If you can't find a bulb which is both the correct size and has the correct sized base, there are E17 intermediate to E12 candelabra adapters available.

  • A G40 is 40 eighths of an inch, a 5" bulb. westinghouselighting.com/light-bulbs/led-bulbs/globes/… Dec 19, 2023 at 3:16
  • @NoSparksPlease I was confused by that too. Bulb numbers are supposed to be in 1/8th of an inch. There's a similar number on the side of the asker's bulb though, and partylights.com/led-g40-professional-bulb-c7-base plus others show this particular size as being a relatively common appliance type bulb, specifically in a medium base.
    – KMJ
    Dec 19, 2023 at 4:55
  • Interesting, after a little digging It appears to me that the lamp you linked is marketed using "Japanese Industrial Standards" vs. ANSI C79.1-2002 (IEC/TR 60887:2010) . I used to drive a 14' cube van doing nothing but lamp and ballast changes in retail stores and never identified anything using JIS. That was before international internet shopping became a thing, I still don't see JIS being widely used, but it is fair the OP should be aware that multiple conventions exist. Dec 19, 2023 at 18:27
  • Also a little odd is this image seems to bounce from ANSI lamp dimensions for most lamp shapes, but JIS for types G and ST. i.shgcdn.com/36effd01-de9b-42f9-9f90-303b4dde1faf/-/format/auto/… Dec 19, 2023 at 18:33
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    Whoops, I meant intermediate base but typed medium and now it's too late to edit my comment. Still, bulb shapes are clearly a weird world.
    – KMJ
    Dec 19, 2023 at 19:29

Lamps are kind of confusing, a common ANSI convention for lamps uses watts/shape/diameter. The diameter is spec'd in eighths of an inch. See these Amazon searches as examples 60A19, 25T10, 7C7 . (Ballasted lamp types precede W/S/D with a letter like F32t8.)

But then the base isn't part of the number. They are now metric "normalized" dimensions. Edison didn't define the E26 base as an Edison 26mm, it was an Edison 1". An E17 was a 5/8" intermediate base, and an E12 was a half inch candelabra base.

The glass on your bulb lacks a neck, I don't think it's a "G" Globe format, I think it's an "S" Sign format. So if 1.25" lamp in watts/shape/size format would create something like a 40S10. I'm guessing it would actually be a 40s11 since the base looks to me like an intermediate base, but it could be a candelabra.

  • Given the E26 next to it, there's no way that is an E12. It's either an E17 or a weird custom size.
    – KMJ
    Dec 19, 2023 at 19:31
  • Is the 5/8" measurement to the outside edges of the threads? It does not fit in a 5/8" hole, 16mm is too tight and 18mm is too large.
    – Roberto
    Dec 19, 2023 at 22:10
  • I don't know the measure points, just handled so many that identification by appearance is easy. But maybe you've dealt with old style 7c7 candelabra base Christmas/night lights and you can recall the definite size difference. The other point of observation is the taper of the insulating material between the tip and screw is usually is usually sharper on E12's than yours appears. Dec 20, 2023 at 0:02
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    @Roberto the measurements are in my answer, from a manufacturer of similar bulbs. If it's a half mm off it's fine, it will fit. Unless this is something weird and custom it's going to be one of four screw base sizes, and they're all pretty far from reach other in size. The fact that it's between 16mm and 18mm is another good sign for it being E17 base.
    – KMJ
    Dec 20, 2023 at 5:18
  • Ok I'm going with these that look identical: Lava lamp bulbs
    – Roberto
    Dec 20, 2023 at 14:04

Looks like a medium base (E26/E27). From bulbs.com

You can also buy an adapter to convert medium base to candelabra. Amazon conversion

  • A19 is normally E26. This bulb is clearly smaller. Dec 18, 2023 at 23:28
  • A19 is apparently bulb size. E26 is base size. I only considered the base, which appears to be a medium to me. (I measured on screen, took ratio, and came up with medium base). Bulb sizes are smaller with smaller base bulbs, so finding a bulb to fit might be easier in candelabra base size.
    – RG Hughes
    Dec 19, 2023 at 0:42

That is an A15 candelabra base. Very common lamps. About a 50-50 mix with the medium base A15 in appliances.


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