SAE Code 61 vs Code 62 Flanges: Pressure and Pattern Basics

SAE Code 61 and Code 62 flanges are common four-bolt hydraulic flange connections. They both use an unthreaded female port with four bolt holes and a male flanged head with an O-ring groove.

The O-ring is compressed between the flanged head and the flat surface around the port. Bolts hold the flange connection together and maintain the sealing load.

Code 61 and Code 62 Pressure Classes

Code 61 is the standard-pressure series. Depending on size and exact specification, Code 61 fittings are used across a range of pressures and are common in many fluid power applications.

Code 62 is the heavy-duty series. It is built for higher pressure service and is commonly associated with applications up to about 6,000 psi, depending on size and rating.

The Designs Look Similar

Code 61 and Code 62 flanges share the same basic connection idea, but the flange head diameter, bolt hole spacing, and pressure capability differ. A part that looks close should not be treated as a match.

The higher-pressure Code 62 style uses larger dimensions in key areas. Mixing Code 61 and Code 62 components can create leakage or a serious pressure failure.

Caterpillar-Style Flanges

Caterpillar-style flanges are frequently used on pumps and motors in fluid power equipment. They follow the same general four-bolt flange concept, but dimensional details must be checked.

Caterpillar flanges may share the same flange outside diameter as SAE Code 62 while using a thicker flange head. That detail can matter during replacement.

Interchangeability and Bolt Sizes

SAE J518, DIN 20066, ISO/DIS 6162, and JIS B 8363 flange families are often discussed together. Some dimensions are interchangeable, but bolt sizes and selected details may differ.

Before replacing a flange, confirm the exact standard, code, bolt pattern, flange head thickness, O-ring size, and port face.

Komatsu Flange Notes

Komatsu flange fittings are very close to SAE Code 61 flanges and are often discussed as interchangeable in body geometry. The important caution is the O-ring size.

When substituting an SAE fitting into a Komatsu-style connection, verify the correct SAE O-ring and the full connection specification. A matching bolt pattern alone is not enough.