SEIKO Original Case Gasket (1 piece) / O-Ring Ref. EZ1825B – Genuine Seiko Packing (WP)

Original SEIKO housing seal (O-ring) with reference EZ1825B , supplied in the original SEIKO WP spare parts bag (純正部品).
This is a factory- and housing-specific NOS spare part , as intended by SEIKO for assembly and overhaul – not a generic seal .

This gasket is typically used as a bottom gasket and is designed for SEIKO enclosures with a precisely defined groove geometry. Correct assignment is only possible via the SEIKO packing code .

Technical specifications

• Manufacturer: SEIKO
• Replacement part type: Housing seal / O-ring (Packing)
• Part number: EZ1825B
• Material: Synthetic rubber (SEIKO specification, oil and age resistant)
• Color: Black
• Condition: NOS (New Old Stock), unused
• Scope of delivery: 1 piece in original SEIKO bag
• Origin: Japan

Exact allocation & use

The reference EZ1825B belongs to the SEIKO packing code system for case gaskets and is used in numerous SEIKO models (especially vintage/neo-vintage) where:

• a round O-ring bottom seal
• with precisely defined internal and external dimensions
• as well as specified material and hardness specifications

is planned.

⚠️ Note:
Seiko does not assign specific models via model names, but rather via case and movement references . Therefore, this gasket is not universally interchangeable . A dimensional or code check is strongly recommended before installation.

Explanation of the SEIKO packing coding system (example: EZ1825B)

SEIKO uses a systematic coding scheme for seals that clearly describes shape, size, strength and material.

Structure of part number EZ1825B

1. First letter – Form code

• E = Round seal (O-ring, circular)

2. Second letter – Cross-section/profile code

• Z = Standard O-ring profile according to SEIKO standard
  (round cross-sectional shape for floor seals)

3. Four-digit number – size indication

• 1825 = Nominal diameter of the seal
  → corresponds to the inner diameter or reference dimension of the housing groove (SEIKO internal measurement system, not directly mm-identical)

4. Last letter – Material/hardness code

• B = Standard SEIKO elastomer
  (proven mixture for housing seals, good aging and pressure resistance)

➡️ Result:
EZ1825B = round SEIKO bottom seal with defined size and material quality for waterproof housing constructions.

Installation note

• Only install using suitable sealing grease (e.g. silicone grease).
• Remove old seal completely
• Clean the housing groove before assembly
• Do not stretch or twist the seal.

Note regarding water resistance

Installing a new original seal alone does not guarantee watertightness.
For a reliable seal, the condition of the case, back, glass and crown are also crucial.