Deciphering SEIKO Part Numbers
SEIKO Model, Case and Part Number Codes
How to read and interpret SEIKO codes, including some common Part Numbers as well as Model and Serial Numbers.
This article includes tools to help decode common part numbers to help find generic replacements, interpret model and serial numbers to determine caliber and date of manufacture, and a transcript of SEIKO's manual on case and gasket coding for reference.
Table of Contents
Part Number Decoders
- Gasket Part Number Decoder
- Crystal Part Number Decoder
- Model Number Decoder
- Serial Number Decoder
- Crown Part Number Decoder
Gasket Part Number Decoder
Enter your gasket code here to decode the size, shape and other qualities. This will help you find a matching after-market gasket equivalent.
Cross Section | Width | Size | Color tone | Shape | Serial No |
Part Number Scheme | |
Width
Thickness |
|
Size
Inner Dimension |
|
Color | |
Shape | |
Cross Section | |
Material | |
Serial No |
Where to find a Gasket Part Number
Use the Model Number Decoder (click here) for parts listings on either Jules Borel or Boley. Locate the part number for the gasket in question and enter it in the decoder above. Be sure to find the original part number. Replacement part numbers are typically also listed, but these do not follow SEIKO's part number scheme and cannot be decoded here.
Crystal Part Number Decoder
Enter your crystal part number here to decode the size, shape and other qualities. This will help you find a matching after-market crystal equivalent. Be sure to set the Part Number Scheme option to reflect the manufacture year of your watch, either before 1990 or from 1990 onward.
Size (Diameter) | Type | Serial No | Material | Finish | Color Tone | Shape / Sub |
Size
Diameter |
|
Type | |
Serial No | |
Material | |
Finish | |
Color Tone | |
Shape / Sub |
Where to find a Crystal Part Number
Use the Model Number Decoder (click here) for parts listings on either Jules Borel or Boley. The Model Number Decoder (click here) will also attempt to identify the correct crystal part number based on the model number. Locate the part number for the crystal in question and enter it in the decoder above. Be sure to find the original part number. Replacement part numbers are typically also listed, but these do not follow SEIKO's part number scheme and cannot be decoded here.
Model Number Decoder
And Part Number Finder
The model number is found on the case back and should be an 8-digit sequence of numbers and/or letters, in two segments. Here are some valid model numbers: 6217-7000, A239-502A, M158-5009, etc.
Movement Code | Case Code | Region |
Movement Caliber |
|
Case Code | |
Region Code | |
Crystal Part Number | |
Jules Borel Parts List | |
Boley Parts List |
Where to find the Model Number
The model number is located on the case back, noted in two 4-digit segments. Here are some examples.




Serial Number Decoder
The serial number is found on the case back and should be an 6-digit or 7-digit sequence of numbers and/or letters.
Year of Production | Month of Production | Production Sequence Number |
Production Year |
|
Production Month |
|
Production Number |
Where to find the Serial Number
The serial numbers is located on the case back, as a series of numbers with either 6 or 7 digits. All digits will be numeric, except perhaps the second digit, which may be numeric or also an N or D. Here are some examples.




Crown Part Number Decoder
Older Seiko Crown Part Numbers were 8 alpha numeric digits, newer codes are 10-digits. Select which type of code you are entering (8 or 10 digits) and paste or type the code to decode the crown part number's properties.
Size | Type | Serial Number | Finish | Color tone | Assortment |
Size |
|
Screw Diameter |
|
Type |
|
Serial No | |
Material | |
Finish | |
Color tone | |
Assortment | |
Sub |
Where to find a Crown Part Number
Use the Model Number Decoder (click here) for parts listings on either Jules Borel or Boley. Locate the part number for the crown in question and enter it in the decoder above. Be sure to find the original part number. Replacement part numbers are typically also listed, but these do not follow SEIKO's part number scheme and cannot be decoded here.
SEIKO Coding Document Transcribed
First, here are the source documents:
The following text has been modernized, reformatted and re-purposed from the document scans above. Most of the wording is lifted from the originals, updated and corrected as errors are found.
Crystal Part Number Coding
The structure of the parts number for the glass is classified into two groups according to the shape of the glass, that is, whether the glass shape is round or not.
Round Glass (10 digits)
Round glass / crystals are codes in the following segments:

NOTE: In the coding system for glass, type code and finish code have been revised from 1990 for new models. The following examples show the pre-1990 and post-1990 coding changes.


Size Code
The Size Code shows the glass diameter in three numerical digitals. For Example:

Type Code
The Type Code is expressed in one letter.
-OLD-
No accessory | With tension ring | With ring or bezel | With other accessory | |
---|---|---|---|---|
Water Resistant | W | T | V, G | X |
Non-water Resistant | N | D | R | Y |
-REVISED-
The following two letters are newly used to identify the mounting structure of the glass.
"N" and "W", which were used so far to denote the water resistant quality, have been replaced by the new classification.
- A: Bonded
- P: Pressed in using plastic gasket
For Example
Old | New |
---|---|
200N21SN01 | 200A01SN01 |
RE0W15JN02 | RE0P01JN02 |
NOTE: "N" and "W" will still be used for glasses having other types of mounting structure such as welded glass.
Serial No. Code
A number from 01 to 99 is assigned for the purpose of production-related classification.
Material Code
Expressed in one letter, as follows:
- A: Acrylic glass
- E: Acrylic glass/others
- G: Hardlex glass (Inorganic tempered glass)
- H: Hardlex glass (Inorganic tempered glass)
- J: Hardlex glass (Inorganic tempered glass)
- K: Hardlex glass (Inorganic tempered glass)
- L: Hardlex glass (Inorganic tempered glass)
- S: Sapphire glass
- Z: Others
Finish Code
Expressed in one letter, as follows:
No-treatment | Treated | |||||
---|---|---|---|---|---|---|
Printed | Evaporated | |||||
Classifications | Old | Revised | Old | Revised | Old | Revised |
Ordinary finish | N | ← | M | * | V | * |
Cut | C | N | H | * | J | * |
Curved | K | N | U | * | R | * |
No reflection coating | B | * | G | * | W | * |
Antistatic coating | D | * | P | * | T | * |
Ion plating treatment, etc. | E | * | Z | * | L | * |
Anti-fogging coating | A | ← | F | ← | Y | ← |
NOTE:
- * .......... A numeral (from 1 to 9) or a letter of the alphabet (M, V, H, J, R and S) is assigned in the order in which the code is established.
- Curved glass (K) and cut glass (C) are newly classified as ordinary glass (N).
Color Tone Code
Expressed in one letter, as follows:
- M: Green
- L: Blue
- P: Pink
- V: Violet
- Y: Yellow
- O: Transparent
- S: Transparent w/ silver color ring
- G: Transparent w/ gold colored ring
- E: Others
Shape Code
One letter to show the cross section of the glass.
There are a great variety of cross sections, and the following are typical examples.



Sub Code
One numerical digit to show the slight difference in color tone.
Shaped other than round glass (10 digits)
The first three digits have a different meaning from those for the round shaped glass.

NOTE: In the coding system for glass, type code and finish code have been revised from 1990 for new models. The following examples show the pre-1990 and post-1990 coding changes.


Shape Codes
Expressed in two letters to show the plane view of glass.
The following gives typical shapes.
Shape | Code | Description |
---|---|---|
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AL | Almond |
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TD | Teardrop |
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SQ | Square |
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RE | Rectangle |
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BA | Barrel |
![]() |
KO | Oval |
![]() ![]() |
SA | |
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WA | Lozenge |
N/A | ES | Other |
Serial No. Code
A number from 0 to 9 is assigned for the purpose of production-related classification.
Gasket Part Number Coding
Gasket codes are classified into three groups as follows:
-
Non plastic gasket (9 digits)
-
Previous coding system
The 3rd and 6th digits are numerical in the previous system. -
New coding system
The 3rd and 5th digits are numerical in the new system
-
Previous coding system
-
Plastic gaskets (8 digits)
- Coding system of "OTHER CASING PARTS" on page 14.
Previous Coding System (9 digits)


Cross Section Code
One alphabetical digit to show the shape of the cross section
Shape | Code | Description |
---|---|---|
![]() |
A | A-shaped |
![]() |
D | D-shaped |
![]() |
F | Square shaped |
![]() |
B | B-Shaped |
![]() |
O | O-shaped |
N/A | E | Other |
Width Code
One alphabetical letter to show the cross section width.

Example values are:
- A: 0.60mm
- B: 0.75mm
- C: 0.90mm
- D: 1.05mm
- E: 0.85mm
- F: 1.30mm
- G: 0.40mm
- H: 0.50mm
- I: 0.55mm
- J: 0.80mm
Size Code
Four numerical digits to show the inside diameter of the gasket between 9 o'clock and 3 o'clock sides.

Example values are:
- 2980: 29.8mm
- 2920: 29.2mm
- Etc.
Color Tone Code
One alphabetical letter to show the color of the gasket, as follows:
- B: Black
- L: Blue
- N: Grey
- O: Transparent
- W: White
- Y: Yellow
- E: Others
Shape Code
One numerical digit to show the plan view of the gasket. If a parts number is given 7-digits, the shape code is omitted.
Shape | Code | Description |
---|---|---|
![]() |
0 | Circle |
![]() |
1 | Square |
![]() |
2 | Rectangle |
N/A | 3-9 | Other Shapes |
Serial No Code
A number from 1 to 9 assigned to differentiate the shapes and materials. In cases with 7-digit notation, the serial no code is omitted.
New Coding System (9 digits)


The new coding system retains the previous codes for the following:
- Cross Section Code
- Color Tone Code
- Serial No Code
Width Code
Example width code values for the new coding system are as follows:
- A: Less than 0.19mm
- B: 0.20 - 0.29mm
- C: 0.30 - 0.39mm
- D: 0.40 - 0.49mm
- E: 0.50 - 0.59mm
- F: 0.60 - 0.69mm
- G: 0.70 - 0.79mm
- H: 0.80 - 0.89mm
- J: 0.90 - 0.99mm
- K: 1.00 - 1.09mm
- L: 1.10 - 1.19mm
- M: 1.20 - 1.29mm
- N: 1.30 - 1.39mm
- P: 1.40 - 1.49mm
- R: 1.50 - 1.59mm
- S: 1.60 - 1.69mm
- Z: More than 1.70mm
Size Code
Example size code values for the new coding system are as follows:
- 298: 29.8mm
- 012: 1.2mm
- 007: 0.75mm
Shape Code
Example shape code values for the new coding system are as follows:
- A: Circle
- B: Square
- C: Rectangle
- D: Gable (generally triangular)
- Z: Others
Material Code
Material codes are missing the scanned source documents and images. If you have a copy of this missing information, please reach out!
Crown Part Number Codes
There are old (8 digit) and new (10 digit) coding systems.
Old 8-Digit Codes


Size code
Two numerical digits to show the outside diameter of the crown.
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Example value: 35 = 3.5mm |
Type Code
One letter to designate the crown function
Water resistant crown |
M-Type
Gasket is provided outside |
![]() |
|
W-Type
Gasket is provided inside |
![]() |
||
E-Type
with stem |
![]() |
![]() |
|
Non-water resistant crown |
N-Type
Ordinary design |
![]() |
|
D-Type
with dust-proof pipe |
![]() |
||
S-Type
with dist-proof spring washer |
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||
R-Type
with gasket |
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||
E-Type
Others: Stopwatch, etc. |
Serial No code
A number from 01 to 99 is assigned to differentiate the appearance.
Finish code
Expressed in one letter to desgnate the surface finish of the crown.
- N : Ordinary finiah
- D : Diamond-cut finish
- E : Others
Color tone code
One letter to show the material and the kind of surface plating.
A, B, D, F, N | SGP (Gold tone) |
C | CRP (Chromium plating) |
E | 18K (18-carat yellow gold) |
X | 18K (18-carat white gold) |
J | PDP (Palladium plating) |
M | 14KWG (14-carat white gold) |
S | Stainless steel |
Z | 14K (14-carat yellow gold) |
Assortment code
One numerical digit or letter to show the type of marking on the crown.
1 | without mark |
![]() |
2-3 | with mark |
![]() |
4-9 | Others | |
A-E | with jewel |
New 10-Digit Codes


Screw diameter code
A numeral to identify the type of screw that fits the winding stem.
- 1 : No screw
- 6 : 60P15
- 8 : 80P20
- 9 : 90P22.5

Type code
A letter excluding I, O, Q and U to classify the type of crown.
A-Type
Dust-proof (without gasket) |
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|
E-Type
Screw lock type with winding stem (High-pressure water resistant) |
![]() |
|
K-Type
With a fixing ring (High-pressure water resistant) |
![]() |
|
M-Type
Gasket makes contact with the inside of the winding stem pipe (Water resistant, Non-water resistant) |
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|
E-Type
Others: Stopwatch, etc. |
Size code
The first two figures of the outside diameter of a crown.
![]() |
Example value: Outside diameter 325 (3.25mm) = Size code 32 |
Serial No. code
Consisting of two digits; a letter excluding I, O, Q and U for the first digit and a numeral for the second digit.
Material code
A letter excluding I, O, Q and U to denote the material of the crown head.
- B : Brass
- K : 18K (* Color of gold is classified by the color tone code.)
- M : 14K (* Color of gold is classified by the color tone code.)
- N : Ns (Nickel silver)
- P : Plastic
- S : Stainless steel
- T : Titan
- Z : Others
Finish code
A letter excluding I, O,Q and U to denote the finish of the roulette and head of the crown.
Color tone code
A letter excluding I, O,Q and U to denote the color tone of the crown head.
Sub code
Consisting of a numeral and a letter excluding I, O, Q and U that denote the difference in color tone, material and color tone of jewel and marking. The numeral is assigned in the order in which the code is established.
World Time Part Numbers
The following parts charts are focused on consumable parts, like gaskets and crystals. Click on the model no in the first column to open a new tab to the Jules Borel database, which contains additional part numbers.
Generation 1: Mechanical Watches
Model No | Crystal / Glass | Caseback Gasket |
---|---|---|
6217-7000 | 341W02AN | 0C3060B0A |
6217-7010 | 350W02AN | 0C3280B01 |
6117-6010
6117-6019 |
340T06ANS0 or 340T06AN | FH2920B01 |
6117-6400
6117-6409 |
350T02ANS or 350T02ANG | FH2980B01 |
Generation 2: Digital Watches
Model No | Battery | Crystal / Glass | Crystal Gasket | Caseback Gasket | Battery Hatch Gasket | Pusher Gasket | Pusher Retaining Clips |
---|---|---|---|---|---|---|---|
M158-5000
M158-5009 |
SR1130W | BA0W66GN00 |
8617.9900 (black)
8617.9901 (brown) |
FZ2960B0 | EH1175B01 | DJ0060B01 | TBD |
A358-5000
A358-5009 |
SR1120W | SA1W24GN00 | 86178920 | 0Z2701B01 | N/A | 0A0064B01 | TBD |
A239-5000
A239-5009 A239-5010 A239-5020 A239-502A |
SR927W | ES0W81HN00 | 86171300 | 0B2910B04 | 011140B0A | TBD | TBD |
A708-5000
A708-5010 |
CR2016 | SA7W06GN00 | 86571820 | TBD | N/A | EG0060B01 | 83200271 |
A718-5010 | CR2016 | ES6W18GN00 | 86571460 | FH2980B01 or FH2980B0A | N/A | EC0060B0A | 83200271 |
A718-5030 | CR2016 | SA3W92GN00 | 86571380 | TBD | N/A | EG0060B01 | 83200271 |
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