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 July 2017
Caliber 440 Curvex Movement 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. 

The serial number, only 4-digits long and seemed useless.... until a prefix is added 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!

Rather than repair a broken balance staff, it's quicker, easier and cheaper to swap out the entire movement (sometimes).  

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 table is incomplete, but it's a start that we can use to get the ball rolling

The GruenWristwatches Caliber 440 Serial Number Date Table

Serial  Date
0       1940
4,100   1942
5,000   1943
7,400   1944
A 0000  1945
B 0000  1948
C 0000  19??

Want to see what the raw serial number data looks like so you can join the fun in cracking this 440 movement series or so you can draw you own conclusions?  Well, here's all the data presented in a nice graphical format.  You can play with this data, exclude datapoints, download the entire table that's driving it all.

This is a scatter plot.  The serial numbers are graphed along the bottom / the X axis.  The Wadsworth serial numbers are on the Y-Axis.  Simply removing the "G" gives us that number.  However, the L series of cases were the series that FOLLOWED the G series.  So, those serial numbers have 1,000,000 added to them to normalize them to the G series.

I colored the data points using the 440 Serial Number Prefix.  For blank they're green, A is red, B is yellow and C is blue.

If movements were RANDOMLY placed into Wadsworth cases, you would expect to see the colored dots to span the entire range of Wadsworth numbers, but we don't see this.  Instead, each prefix lives within a "band" or range of case serial numbers.

On data massaging.....
There are clearly some BAD data points in this table.  These are cases where the original movement was swapped out and thus can no longer be used for this analysis.  The easiest to see example is #9714.  Find that sample on the graph and you'll see it has a case serial of G311140 paired with it.  This movement's number is just before the rollover to the A-series.  I think this rollover happened around 1945.  This #9714's case is from about 1943, too early.

What needs to happen is a cleanup of the data.   The datapoint that are clearly whacked should be tossed out.  It's valid for us to bring common sense and what we've learned to the party and utilize it to get the data samples as close to reality as possible.

How the data SHOULD look.  There should be a gradual trend in an upward and to the right direction from one data point to another.  GIANT numerical jumps are indicators of bad data. There will be SOME wiggle room as movements and cases are BOTH inventoried items, meaning that they could sit for X amount of time before being used.  Example...maybe a batch of 440 movements came over and was enough to last 2 years.  Then, when a watch is ready to be made, perhaps the case serial number is current/fresh, but the movements in the inventory are 2 years old.  Right there we'll have a potential gap/jump in the data.  We know SOME amount of inventory was kept on hand, but it's rare for any company to have a LARGE number of years worth of inventory.  But, one must keep in mind that the environment these watches was made in was nothing but normal.  Gruen had to deal with supply problems during World War II and the inventory levels they desired would surely be as large as possible to smooth over any future supplies hiccups. 

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

Wadsworth Case Serial Numbers

In addition to the movement serial numbers, cases made by Wadsworth can sometimes be used to date a watch.  Check out the Wadsworth Case Serial numbers page in the Reference Section.

Download a PDF version of the table movement serial number table