SAE Flange Fittings: Code 61 vs Code 62 Explained
On larger hydraulic lines, where a threaded fitting would be impractical or leak-prone, four-bolt SAE flanges take over. There are two families, Code 61 and Code 62. They look similar and they do not interchange. This guide explains the difference and how to specify the right one.
What is the difference between SAE Code 61 and Code 62 flanges?
The short answer: both are four-bolt split flange connections to SAE J518, but Code 61 is the standard-duty series rated to about 3,000 psi and Code 62 is the heavy-duty series rated to about 6,000 psi. Code 62 has a thicker flange head and a larger bolt pattern for the same nominal size, so the two are not interchangeable. Mixing them gives an unsafe joint.
How a four-bolt flange seals
Instead of a thread, a flanged port uses a flat flange face with an O-ring, clamped down by two split flange halves and four bolts. The O-ring does the sealing; the bolts provide the clamping force. That makes flanges well suited to large-bore, high-pressure and high-vibration lines where threads are hard to seal and tighten.
Code 61 (standard duty)
Code 61 is the 3,000 psi series (ratings taper down at the largest bore sizes). It is the most common flange in general hydraulics and mobile equipment.
- Choose it for: pump and motor ports and general high-flow lines up to its pressure rating.
Code 62 (heavy duty)
Code 62 is the 6,000 psi series, with a heavier flange head and wider bolt spacing than a Code 61 of the same nominal size.
- Choose it for: high-pressure circuits, and any application where the pressure exceeds what Code 61 can hold.
Why they must not be mixed
Because the bolt patterns and flange thicknesses differ, a Code 61 clamp will not correctly fit a Code 62 flange head, or the reverse. Forcing a mismatched pair gives uneven clamping and a joint that can leak or fail under pressure. Always confirm the code on both halves.
Comparison
| Code 61 | Code 62 | |
|---|---|---|
| Standard | SAE J518 | SAE J518 |
| Duty | Standard | Heavy |
| Typical rating | ~3,000 psi | ~6,000 psi |
| Flange head | Thinner | Thicker |
| Bolt pattern | Narrower | Wider |
| Interchangeable | No | No |
SAE J518 is dimensionally compatible with ISO 6162 for the flange itself, but bolt thread standards (UNC versus metric) can differ, so confirm the bolt spec too.
Related range: Browse Velqor flange fittings →
The goal is a flange joint that holds, whether you buy from us or not
We wrote this so you can tell Code 61 from Code 62 and specify a flange that matches your pressure, wherever you source it. Check the pressure rating and the bolt pattern; never assume two flanges mate just because the bore matches.
If you do want it sourced to spec, here is how we work: Velqor supplies SAE Code 61 and Code 62 flange fittings and split flange halves matched to your port, pressure and bolt standard, confirmed and tested before dispatch. Tell us the pressure, size and whether the bolts are UNC or metric, and we will confirm the correct code rather than guess.
Frequently Asked Questions
Can I bolt a Code 61 clamp onto a Code 62 flange?
No. Code 62 uses a thicker flange head and a wider bolt pattern, so the two do not fit together. A mismatched pair clamps unevenly and can leak or fail. Match the code on both halves.
What pressure are Code 61 and Code 62 rated for?
Code 61 is the standard-duty series, commonly rated around 3,000 psi, and Code 62 is the heavy-duty series, commonly rated around 6,000 psi. Ratings taper down at the largest bore sizes, so check the size-specific figure.
What seals a four-bolt flange, the bolts or an O-ring?
The O-ring between the flange face and the port seals; the four bolts and split flange halves provide the clamping force. Even bolt torque in the correct sequence matters for a leak-free joint.
Is SAE J518 the same as ISO 6162?
They are dimensionally compatible for the flange itself, but bolt thread standards can differ (UNC versus metric). Confirm the bolt specification when mixing SAE and ISO parts.
When should I use a flange instead of a threaded fitting?
On large-bore, high-pressure or high-vibration lines, and at pump and motor ports, where threads are difficult to seal and tighten. Flanges spread the clamping load and are easier to make and break on big lines.