Technical Guide

SAE Flange Fittings

Code 61 & Code 62 Explained

SAE flange fittings (SAE J518) explained: Code 61 vs Code 62, bolt circle diameters (BCD), flange sizes, and how to specify them correctly for high-pressure, high-flow applications.

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How to Identify an SAE Flange

SAE flanges are identified by size, pressure code, and bolt circle diameter. Follow these steps to specify the correct flange.

Determine the Flange Size

SAE flanges come in standard sizes: 1/2″, 3/4″, 1″, 1-1/4″, 1-1/2″, 2″, 2-1/2″, 3″. The size refers to the nominal bore of the flange, which corresponds to the hose/tube size.

Identify the Pressure Code (Code 61 vs Code 62)

Code 61 (3000 psi series): standard pressure flange. Code 62 (6000 psi series): high pressure flange with a thicker flange head and larger bolt circle. Look at the flange thickness and bolt pattern — Code 62 has a larger bolt circle diameter (BCD) for the same size.

Measure the Bolt Circle Diameter (BCD)

The BCD is the diameter of the circle that passes through the centers of the bolt holes. Code 61 1/2″: 30.2mm BCD | Code 62 1/2″: 31.8mm BCD. Code 61 3/4″: 38.1mm | Code 62 3/4″: 41.3mm. Code 61 1″: 44.4mm | Code 62 1″: 47.6mm. Measuring BCD is the most reliable way to distinguish Code 61 from Code 62.

Count the Bolt Holes

All SAE flanges have 4 bolt holes (4-bolt pattern). Some special flanges (2-bolt flange clamps for heavy-duty) exist but the standard SAE J518 flange is always 4-bolt.

Check the O-Ring Groove

SAE flanges seal with an O-ring in a groove on the flange face. The O-ring sits in the groove and seals against the mating port face. Check that the O-ring groove and O-ring are present and in good condition.

Check Bolt Size

Flange bolts are sized by diameter and thread. Code 61 uses UNC bolts (imperial). Code 62 uses slightly larger bolts for the higher pressure. Bolt sizes: 1/2″ flange: 5/16″ bolt | 3/4″: 3/8″ | 1″: 3/8″ | 1-1/4″: 7/16″ | 1-1/2″: 1/2″ | 2″: 1/2″.

Technical Specifications

1/2" Flange	Code 61: 30.2mm BCD, 5/16″ bolt \| Code 62: 31.8mm BCD, 5/16″ bolt
3/4" Flange	Code 61: 38.1mm BCD, 3/8″ bolt \| Code 62: 41.3mm BCD, 3/8″ bolt
1" Flange	Code 61: 44.4mm BCD, 3/8″ bolt \| Code 62: 47.6mm BCD, 3/8″ bolt
1-1/4" Flange	Code 61: 50.8mm BCD, 7/16″ bolt \| Code 62: 54.0mm BCD, 7/16″ bolt
1-1/2" Flange	Code 61: 60.3mm BCD, 1/2″ bolt \| Code 62: 63.5mm BCD, 1/2″ bolt
2" Flange	Code 61: 71.4mm BCD, 1/2″ bolt \| Code 62: 79.4mm BCD, 5/8″ bolt
2-1/2" Flange	Code 61: 84.1mm BCD, 1/2″ bolt \| Code 62: 90.5mm BCD, 5/8″ bolt
3" Flange	Code 61: 95.2mm BCD, 5/8″ bolt \| Code 62: 108.0mm BCD, 3/4″ bolt
Standard	SAE J518 (Code 61 and Code 62) — flange dimensions
Pressure Rating	Code 61: up to 34.5 MPa (5000 psi) working \| Code 62: up to 41.4 MPa (6000 psi) working

Code 61 vs Code 62 — Which One?

Code 61 and Code 62 flanges look similar but are NOT interchangeable. Here are the key differences: Code 61 (3000 psi series): - Standard pressure flange - Thinner flange head - Smaller bolt circle diameter (BCD) - Used in most general hydraulic applications Code 62 (6000 psi series): - High pressure flange - Thicker flange head (about 1.5x thicker than Code 61) - Larger BCD for the same nominal size - Used in high-pressure applications (heavy machinery, presses) For the same nominal size, Code 62 always has a larger BCD. If you're replacing a flange and not sure which code, measure the BCD and compare against the specs above.

How to Measure BCD

Bolt Circle Diameter (BCD) is the diameter of the circle passing through the centers of all bolt holes. How to measure: 1. Measure the distance between the centers of two bolt holes that are diagonally opposite (for 4-bolt flanges). 2. This diagonal distance is the BCD. Alternatively: 1. Measure the distance between the centers of two adjacent bolt holes. 2. For 4-bolt flanges, multiply this distance by 1.414 (√2) to get the BCD. Example: If adjacent bolt holes are 21.3mm apart, BCD = 21.3 x 1.414 = 30.1mm (approximately 30.2mm — this is a Code 61 1/2″ flange). Accurate BCD measurement is the most reliable way to identify the flange. When in doubt, send us a photo with a ruler for scale.