Writen by Bill Meier
There are often dots present after the year code. A dot was added for each additional year of production after the mold was made. Generally, these were neatly aligned in two rows after the year code, looking like a row of colons. But, a colon is really two dots. In some cases the dots are around, above, and below the "-" dash. In any case, count ALL the dots, and add this to the mold year (see above). This gives the date the insulator was actually produced.
The mode code is a one or two digit number, sometimes followed by a letter. In some cases, the letter designated the type of material the mode was made out of. Generally, the mold code is not significant, unless you really are a specialty collector.
In the table below MM represents a mold number (not a month), and Y or YY represents a one or two digit year. Dots will likely follow the "numbers". This is discussed in following paragraph.
|Style||Front Skirt||Rear Skirt||Date of Mold
|Date of Insulator
|1||O||(nothing)||1933||Count the dots around
the year code and add
them to the date computed
in the column to the left.
|2||O-Y||MM||1930 + Y||MM|
|3*||(nothing)||MM - YY||1900 + YY||MM|
|4||(nothing)||MM - MADE IN U.S.A. - Y
(this format is on many CD 230's)
(Y is often 0, which is 1940)
* Note with style 3, YY may still be a single digit, with 9 meaning 1939 and 0 meaning 1940.
All dots around the year code should be counted (a colon counts as two dots), and added to the date of mold manufacture. This gives the actual date the insulator was produced. Style 3 is the most common.
This is an example of style 3. The front skirt has nothing, and the rear
5 - 42 : : : .
MM is 5, YY is 42, and we have 3 colons (each count as 2 dots), and a dot, or 7 "dots". Thus, the mold code is 5, the year the mold was made is 1900 + 42 = 1942 and the insulator was manufactured in 1900 + 42 + 7 = 1949.
There are some variations, but they generally can be deduced from the above patterns. In all cases, counting the dots and adding them to the mold year code produces the date the insulator was actually produced.
Some variations include just a 38 or 39 on the front skirt (for 1938 or 1939). In other cases, just the single digit 9 (rather than the two digit 39) was used to represent the year of 1939 (a transition year) as well as just the single digit 0 to represent the year of 1940.