Movement Serial Numbers
Updated Dec 26,
2013
Gruen Movement Dating using Movement Serial Number
For the 405 Family of Movements
405, 406, 410, 411, 420, 421, 425, 426
The serial number encryption for Gruen
movements in the 405 410 420 & 425 families has been cracked... or so is hoped. Every few months brings new refinements.
This table is for the 405, 420 and 425 based
calibers and is a guide for determining the approximate date of
manufacture of a movement. It’s
most applicable for calibers 405, 406, 410, 411, 420, 421, 425, 426 and
their sweep-seconds versions.
The latest refinement includes extending the table
backwards in time to 1939.
To use these new 1939 and 1940/41 dates, the
movement needs to have these two characteristics:
1. There is nothing written on the ratchet
wheel
2. Veri-Thin is stamped on the “Train
Bridge”
Serial number Year
-------------------------
700,000
1939
900,000
1940/1
This table is the same as the previously published one in 2012, but has been refined to be more accurate.
For 405 406 410 411 420 421 425 426 calibers and their sweep versions
Serial number Year
-------------------------
010,000
1941*
400,000
1942**
750,000
1943/4+
900,000
1945
A 100,000 1945‡
1A 10,000 1945
1B 10,000 1945/6
1C 10,000 1946
A 900,000 1946
B 100,000 1947
B 900,000 1948
C 100,000 1949
C 900,000 1952
Footnotes - To simply use the tables,
you need not concern yourself with these notes.
If you want to really get into the
details of that data derivation then dig in!
*Some low-numbers after the reset continue to have “pre-reset” markings
**Coincident with lowest 405ss/406ss
movements
+ Coincident
with the lowest 420/421 (sub
and SS calibers) observed.
‡Coincident with the highest 405/406 caliber
and lowest of the 425/426 calibers
A few caveats when dating your watch, specifically
when using movement serial numbers:
1 - That
movements could have been made years prior to its incorporation into
your watch. If
this is true for your watch, the
movement will render a date earlier than your watch’s age
2 - Movement swapping is a common repair
method, so
be aware your watch may not contain its original movement and thus the
date will be incorrect
Copyright 2012, 2013 M. Barnett & J. Wood
Download a PDF version of the table movement serial number table
|
Serial Number table 405 420 425 families 2013-12-26 update.pdf Size : 179.105 Kb Type : pdf |
Dating A Gruen Wristwatch from a Wadsworth Case Serial Number
I'm grateful that I can share with you MORE tools for your Gruen toolbelt. Another wrench (spanner for you Brits) in the toolbox is always welcomed as Gruen collectors need all the help they can get.
There are two different case dating methods for Gruen wristwatch cases that were manufactured by Wadsworth. One was developed by Jack Wood, the other Barry Cooper. Both are top-notch Gruen historians and researchers.
These techniques involve looking up a portion of the Wadsworth case serial number in a table to determine the date a Gruen case was manufactured. While these tables appear simple, like all Gruen research work, considerable effort was expended by these individuals to create them.
Before presenting the tables and techniques, a word about case dating....
The Wadsworth case date is the date the watch's case was manufactured. If you want to know the exact age of your watch, then this date is what you are seeking. Let's call this date, the date your Wadsworth case was made, the Wadsworth Date.
If you are attempting to identify your watch, that is, you are seeking the model name and other detailed information about it, then you are actually looking for a different date. For identification research, the critical date is the "Introduction Date", the date the watch model was first introduced to the public for sale. The reason for this is simple; you are most likely to find the most information published about a watch when it first went up for sale. Advertisements and catalogs, the primary source of your identification data, will contain the newest models, not those that have been shipping for 4 or 5 years.
Your Wadsworth Date will be later than the Introduction Date. You will want to look further into the past when searching for detailed data about your watch. More about this can be found in the ID You Gruen! tutorial.
Technique 1 - Serial Numbers that begin with the letter G or L
Jack Wood's article that described how his technique for determining the date a Wadsworth case was made was published in the Sept/Oct 2012 NAWCC journal. Click "Dating a Gruen Wristwatch from a Wadsworth Case Serial Number" to download a PDF copy of the article.
For this particular dating technique, two criteria must be met.
1 - The case must be manufactured by Wadsworth
2 - The case serial number must start with the letter G or letter L
If both of these criteria are not met, then this technique will not work for you.
If your case is a Wadsworth case, and you find a 5 instead of a Gx or Lx at the beginning of the serial number, then you may be able to use the Cooper tables... see Technique 2 below.
See Figure 1 below for how to read a case's serial number that has a G or L prefix.
| Code | Year |
| G0 | 1937-1939 |
| G1 | 1939-1941 |
| G2 | 1941-1942 |
| G3 | 1942-1943 |
| G4 | 1943-1944 |
| G5 | 1944-1945 |
| G6 | 1945-1946 |
| G7 | 1946-1947 |
| G8 | 1947-1948 |
| G9 | 1948-1949 |
| L0 | 1949-1950 |
| L1 | 1950-1951 |
| L2 | 1951-1952 |
| L3 | 1952-1953 |
| L4 | 1953-1954 |
Table 1 - Wadsworth Serial Number Date Table
An example of a Wadsworth manufactured Gruen case that begins with the letter "G"
Technique 2 - Serial Numbers that begin with the number 5
This technique was developed by Barry Cooper, co-author of the Style Number dating paper. His most recent Gruen article was on Tanks and can be found in the members on the NAWCC NAWCC website.
If you're Wadsworth Serial Number didn't have a letter G or L at the beginning, but instead has a 5, then you're in luck! You MAY still be able to find the date the case was made, if it was made between 1925 and 1930.
The first 2 digits of the serial number are used to look up the date in Table 2 below.
Prefix Code Year
50 1925
51 1926
52 1927
52 1928
53 1929
54 1930
Table 2 - Wadsworth serial numbers 1925-1930
This technique provides a date with an accuracy that is +/- 1 or 2 years.
Like so many of the Gruen tools, it is not perfect, has some amount of error, but it works most of the time. In the grand scheme of things, these error amount are minuscule. If you can narrow your watch's date down to a year or two, then you're doing great and likely know a lot more than when you started.
