| Hemingray used mold letters, dome numbers, and even oddly placed periods in some of their earlier insulators to denote which mold an insulator was produced from. It wasn't until 1933, however, that Hemingray began denoting their insulators with specific mold and date codes. Many different codes were used over the years, and I will attempt to explain them all here in relative order.
| 1933 |
| In 1933, Hemingray began embossing a "0" (zero) on the front skirt of certain styles. The "0" is a smaller font size and is typically aligned with the "N" in "Hemingray", either above or below (CD 137 excepted). All known specimens are Ice Blue in color.
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| 1934 |
| In 1934, Hemingray added a "_4" after the "0", the "4" believed to signify "1934".
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| 1935 |
| In 1935, Hemingray added a period after the "4" and added mold numbers to the insulator, typically on the rear skirt above or below "MADE IN U.S.A." Each successive year the mold was used, an additional period was added above, below, or on either side of the "4".
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| 1938 (Version A) |
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I believe this is the earliest form of the 1938 date codes. Similar to the 1934 date code above, the "4" has been replaced with an "8", presumably to signify "1938". A period would also be added after the "8" for each successive year the mold was used.
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| 1938 (Version B) |
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This is another version of the 1938 date code. In this version, they eliminated the "0" and simply put "38", again aligned with the "N" in "Hemingray". A period would also be added after the "38" for each successive year the mold was used.
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| 1938 (Version C) |
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Yet another version of the 1938 date code. In this version, there is only an "8", this time aligned with the "G" in "Hemingray". A period would also be added after the "8" for each successive year the mold was used. So far I have only found this style of date code on the CD 154.
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| 1938 (Version D) |
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This is a unique version of the 1938 date code. First, this type only appears on three Hemingray styles (CD 115, CD 122, and CD 155). Notice that the mold and date have been combined for the first time (in the example below, the mold number is "23" and the date is "38"). What's also unique about this version is that the type is the same size as the main "Hemingray-10" embossing on the front skirt, and "Made in U.S.A." was inexplicably omitted.
In 1939, Hemingray added "MADE IN U.S.A." in smaller letters underneath the unusually large mold and date code, and added a period after the "38" (see below). It appears these molds were only used for two years, as none have surfaced with more than a single period after the "38" (that I know of).
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| 1938 (Version E) |
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This version of the 1938 date code is a hybrid of Version A and Version D, where they combined the mold and date codes together on one side of the insulator, like in Version D, yet only used an "8" to signify 1938, as in Version A.
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| 1939 |
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Identical to the 1938 Version E, using a single digit "9" to denote 1939.
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| 1940 (Version A) |
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Following the pattern of the 1939 version above, this version uses a single digit "0" to denote 1940. Do not confuse this with the original "0" used in 1933! A 1940 "0" will always be found AFTER the dash and on the REAR skirt, whereas a 1933 "0" will always be found BEFORE the dash and on the FRONT skirt.
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| 1940 (Version B) |
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Similar to Version A above, a few Lowex and Hemingray molds were produced with this unique embossing. In this example, the "1" is the mold number and the "0" is believed to signify "1940" ("512" is the style number in this case). As with Version A above, do not confuse this with the 1933 "0"! This particular version of the mold and date code is found only on CD 216, CD 230, and CD 299.7.
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| 1938 1967 |
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This is the most modern and commonly seen version of the mold and date code, and the easiest to decypher as well. In this version the mold number is to the left of the dash, and the date is the two digits on the right side of the dash opposite the mold number. In each successive year a mold was used, a period would be added somewhere beside, above, or below the date. So, an insulator with a date code of "41:::." would mean that insulator was produced in 1948 (1941+7 dots).

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If you made it all the way through all of that and actually understood it all, then congratulations! You deserve some kind of award!
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