Identifying Screw Bases
Serving the United States of America
IDENTIFYING COMMON SCREW BASES*
We know very well that trying to identify a halogen bulb, for instance, that has a small threaded base can be quite a puzzle. Where and how does one measure? How precise does the measuring instrument have to be? How much experience in measuring does one need in order to be proficient in declaring the correct diameter of the base? Finally, the most disturbing question of all: Is the nominal diameter of the base a reference to the base of the bulb or to the socket in which it fits?
HARRINGTON LIGHTS has developed the following field expedient method for identifying these small screw bases and the equipment list below is sufficient to allow correct identification of any of three common bases:
US coins: (2) dimes; (1) penny
Canned Goods with extruded* can: (2) Cans
Flat, Smooth Surface: (1)
Using the coins as spacers, they may be placed as shown below in order to create a gauge between the tops of the cans that will allow identification of the mystery bulb:
First, place the two cans side by side with one dime in front and the other in back of the cans as shown (click image to enlarge):
(While this serves as a very good gauge, you will find that it has other applications as well.)
The gauge shown above will measure a candelabra base between the top rims of the cans without appreciable "wiggle" ; and this is an E12 (12mm), US Candelabra base.
Mini-Can (E11) base: is smaller than the gauge by the thickness of the penny!
E14 European base: is close to the gauge size, but will not pass!
Interpreting the result:
1-13/32" (between 1-3/8" and 1-7/16") = E11, Minican base
1-1/2" = E12, Candelabra base
1-11/16" = E14, European base
If you note the above progression, it is likely that an Intermediate base, E17, will produce a measurement of 1-31/32"; and for practical purposes, your 2" long paper strip will be about the right length without overlapping enough to be marked.
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