Attachment shows 3 different versions of PLOMB embossing on the 3 extensions I have. Can it be determined from the photo approximately when each one was used? I am aware that it would be pre 1948 but can anyone nail it down closer for each one? I have owned these since 1965 but never gave it much thought until I found this great site and started checking the tools I bought during that time, new ones and the used ones like these extensions. TIA for your help.

Newbie Charlie

Made in USA was used on Proto from 1938 or 9 to 1945 and occasionally thereafter till 1948. Proto used date codes but not consistently. They could have been made in different years or with different dies, or in different plants. Unfortunately there are some things we will never figure out.