JIS vs SAE ORB Fittings: Japanese Flare vs O-Ring Boss Port Standard
The key difference: JIS seals metal-to-metal at a 30-degree flare cone. Full breakdown below.
JIS B 2351 uses metric threads with a 30-degree flare for a metal-to-metal seal. SAE ORB uses straight UN/UNF threads with an O-ring boss seal. JIS is standard on Japanese equipment; SAE ORB is the dominant North American port connection standard.
Key Differences
JIS seals metal-to-metal at a 30-degree flare cone.
SAE ORB seals with an O-ring compressed against a machined boss face.
JIS uses metric threads.
SAE ORB uses imperial UN/UNF threads.
JIS is a hose/tube end connection common on Japanese equipment.
SAE ORB is primarily a port connection on North American hydraulic components.
SAE ORB provides better vibration resistance and leak prevention than JIS metal-to-metal sealing.
When to Choose JIS B 2351
Japanese-built equipment where JIS is the OEM standard
Replacement of existing JIS connections
When the equipment manual specifies JIS B 2351.
When to Choose SAE ORB (O-Ring Boss)
North American hydraulic component ports
Applications requiring O-ring sealing reliability
When connecting to US-manufactured pumps, valves, or motors
New system design requiring vibration-resistant port connections.
Practical Notes
The most common scenario where JIS and SAE ORB meet is a Japanese excavator or machine in a North American shop where a component has been replaced with a domestic part having SAE ORB ports. JIS-to-SAE-ORB adapters are available from suppliers that stock Japanese equipment parts. Ensure the adapter O-ring material is compatible with the hydraulic fluid in use.
Common Mistake
Attempting to thread JIS metric fittings into SAE ORB imperial ports. The thread forms and pitches are different. Even if the fitting starts to engage, it will cross-thread and damage the port.
Reference data only. Verify thread dimensions with a thread identification gauge before making connections. Working with pressurized hydraulic systems involves serious injury risks including high-pressure injection, burns, and crushing hazards. This site does not replace manufacturer specifications, proper training, or employer safety procedures. See full terms of use.