Gruen Movement and Case Serial Numbers

Universal Case Serial Number Decoder

Try your luck... maybe your case is in the range of decoded numbers and case makers
Works on Wadsworth, Star, Gruen, Keystone cases.
It will TELL YOU the manufacturer of your case as a verification
Enter serial number without spaces
Like all things Gruen, it's a work in progress and prone to errors (i.e. may the force be with you)

NEW!   Updated Feb 2018
Caliber 440 and 295 Curvex Movements Serial Numbers
Yes, you read that right!!  FINALLY we have more information about the infamous Gruen Curvex movements.  For a very long time, we've been in the dark when trying to locate the date the movement was manufactured. 

Following a year of working on this problem a 'best guess' answer has emerged.  This is my best guess at how to date a men's Caliber 440 and lady's caliber 295 movements.

The serial number, only 4-digits long, seemed useless.... until a prefix was found on the movement which transforms it from useless looking to functional.

Please read the "Identify Your Gruen!" tutorial so that you can put this new information into context.  It's another bit of data to be added to your watch's "date set", in this situation the Movement Manufacture Date.

A word of CAUTION - it is common for watchmakers to swap out the entire movement as a method of repair. This is getting more common as hobbyists are repairing and restoring vintage Gruens now.  This has been great for the community as more running Gruens are entering the market daily. From a statistics standpoint, this practice is disastrous.  It takes away one ability to find the date of a vintage Gruen.  So, before you swap out your movement, think about repairing, please!

It is for this reason that the Movement Manufacture Date is not valid when used in a solitary manner. You'll be correct perhaps as low as 50% of the time.

stated more plainly.... if the ONLY date you have collected about your watch is the 440 caliber's movement manufacture date.... 

You need more dates.  One caliber 440 movement date is not enough to accurately date a Gruen Curvex watch.  There is ONE loophole.... if you are absolutely sure the movement is original (aka this is a new old stock Gruen), then OK, take the risk.  But you better be damned sure it's not been monkeyed with.

The GruenWristwatches Caliber 440 Serial Number Date Table

Serial   Year
     0   1940
  2000   1941
  3000   1942
  6000   1943
  9000   1944
A 0000   1945
A 4000   1946
A 7000   1947
B 0000   1948
B 6000   1949
C 0000   1950
C 2000   1951
C 5000   1952
C 9000   1953

Wristwatch Case Serial Numbers
Cases made by Gruen, Keystone, and Star
Decoding Gruen case and movement serial numbers has been a multi-year, team effort. I want to thank Barry "Bazzab" Cooper, Bernd "Barney" Riemann, and Cathy Orbista for their significant contributions to the project.

While not completed, there has been significant progress this year for Gruen, Keystone, and Star manufactured cases. Prior to this table there was only Wadsworth serial numbers that had been decoded.  There are more prefixes and ranges yet to be completed for these and other case manufactures.  And there are more movement serial numbers to be decoded as well.  All in good time.... this is a great start however!

This table has 3 manufacturers listed - Gruen, Keystone, and Star.  They way it is read is you read the first 2 or 3 characters from the CASE SERIAL NUMBER and locate them in the corresponding columns.  You can then read the year the case was manufactured using the dates going down the table.

|          | Gruen    | Gruen    | Gruen             | Gruen    | Keystone        | Star     |
| Year     | Prefix 4 | Prefix 5 | Prefix B          | Prefix C | Prefix K        | Prefix O |
|          |          |          |                   |          |                 |          |
| 1940     |          |          |                   |          |                 |          |
| 1941     | 42 43    |          |                   |          |                 |          |
| 1942     | 44 45    |          |                   |          |                 |          |
| 1943     |          |          |                   |          |                 |          |
| 1944     | 46       |          |                   |          |                 |          |
| 1945     | 47       | 56       |                   |          |                 |          |
| 1946     |          | 59       |                   |          |                 |          |
| 1947     |          |          | B2 B3 B4 B5 B6 B7 |          | K10 K11 K12 K13 | O36      |
| 1948     |          |          | B8                |          | K14 K15         |          |
| 1949     |          |          | B9                | C1       | K16             |          |
| 1950     |          |          |                   | C2       |                 | O45-O53  |
| 1951     |          |          |                   | C4       |                 | O58      |
| 1952     |          |          |                   | C5       |                 |          |
| 1953     |          |          |                   | C7       |                 |          |
| 1954     |          |          |                   | C9       |                 |          |

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:

 There is nothing written on the ratchet wheel
 Veri-Thin is stamped on theTrain Bridge

Serial number Year

This table is the same as the previously published one in
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
 100,000     1945
1A 10,000     1945
 10,000     1945/6
 10,000     1946
 900,000     1946
 100,000     1947
 900,000     1948
 100,000     1949
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 havepre-resetmarkings
**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
 - 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

Location of serial number on Gruen Watch movement

Download a PDF version of the table movement serial number table

WADSWORTH Case Serial Numbers

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 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.









Table 1 - Wadsworth Serial Number Date Table

Figure 1

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 or 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.