SEIKO Original Housing Gasket / O-Ring – Reference OB2290B (NOS)

Original SEIKO housing gasket (packing/gasket) with reference B2290B , supplied in the original SEIKO packaging.

This is an unused NOS (New Old Stock) spare part from old stock, manufactured according to the SEIKO factory specifications of the time.

This seal was used by SEIKO for classic case designs and is particularly suitable for vintage SEIKO watches of the 1970s and early 1980s that use a flat O-ring seal (e.g. snap-back or press-fit case).

Technical specifications

• Manufacturer: SEIKO
• Original part number: B2290B
• Component: Housing seal / O-ring
• Profile shape: Round (O-ring)
• Inner diameter: approx. 22.9 mm
• Seal thickness: approx. 0.20–0.29 mm
• Material: NBR (nitrile butadiene rubber)
• Color: Black
• Condition: New, unused (NOS – New Old Stock)
• Origin: Japan
• Scope of delivery: 1× original SEIKO seal in original packaging

Usage / Compatibility

This seal was used by SEIKO in, among other things:

• classic SEIKO automatic and quartz models
• Cases with snap-back or press-fit bottoms
• Vintage models with WP marking (Water Proof according to the then SEIKO standard)

⚠️ Note:
Exact compatibility depends on the specific housing and its groove dimensions. Please check the diameter and seal thickness before installation.

Explanation of the SEIKO packaging code system (OB2290B)

SEIKO used a standardized coding system for seals, which allows the most important technical properties to be derived directly from the part number.

1. Profile / cross-section code (first letter)

• B = B型 (B type)
  → round seal, classic O-ring

2. Size code (sequence of numbers)

• 229 → Inner diameter 22.9 mm
  (SEIKO specifies the diameter in 0.1 mm increments )

• The last digit is used for internal classification/tolerance class.

3. Strength code (last letter)

• B = 0.20–0.29 mm

→ very flat gasket , typical for vintage case designs

4. Material & Color

• Black SEIKO seals of this era are usually made of NBR (nitrile rubber).
  → Good oil and aging resistance, true to the original for vintage watches

Summary of the coding

Special features

• Genuine SEIKO spare part , not a reproduction
• NOS quality – ideal for authentic restorations
• Suitable for period-correct servicing of vintage SEIKO watches
• Preservation of the original case design and fit

Note regarding water resistance

Installing a new seal does not guarantee watertightness .
A leak test is generally recommended after installation.