There is no documentation that Plomb marked the year of manufacture on their tools.  We also have no documentation to describe the purpose of the various letters, inverted plumb bobs or other stamping idiosyncrasies on the tools.  Those who knew the meaning - who were present when the tools were marked - are no longer with us.

In the early years of tool manufacture, warrantees were offered for a set period of time as opposed to a lifetime.  The only way to determine if a tool was within the warrantee period was to mark it with the year of manufacture.

John Baldwin examined thousands of Plomb tools to determine if a dating scheme exists.  He concluded that tools manufactured between 1927 and 1942 have stamped indications of their year of manufacture.  John also found that there were occasional deviations from this schedule possibly caused by the individual production divisions.  This was primarily during the depression years of the 1930’s, when management was reluctant to modify still productive stamping equipment. 

Here are the results of John's investigation: 

In the years 1934 and 1939 the change-over was not made on January 1st, consequently tools manufactured in those specific years could be marked with the earlier year.   Year markings were not placed on all tools, but the markings are the only clue to the year.  Other letters and markings do not identify the year of manufacture. 

 

Tools made in 1948 were stamped with the Plomb and Proto names.  This caused a court action with the Plumb Tool Company that resulted in Plomb paying a fine of $250,000 for this stamping.

Here is a pictorial representation of each year, courtesy of Wayne:

 

Copyright 2005-2008. All Rights Reserved

The contents of this site may not be used without prior written consent.