Flanges Fittings

A flange connection is three parts, not one: the flange head on the hose or tube, the split clamp that holds it, and the port flange on the equipment. Bolts supply the preload; an O-ring does the sealing. That split is why flanges are used where a threaded joint would be too large, too slow to service, or too easily loosened by vibration.

Code 61 and Code 62: Same Bolt Pattern, Different Wall

SAE J518 defines two pressure classes that share a footprint. Code 61 is rated to 3000 psi and Code 62 to 6000 psi. The same nominal size uses the same four-bolt pattern and the same bolt spacing, but the flange head is thicker and the O-ring groove differs. Because the footprint is identical, a Code 61 head will physically bolt to a Code 62 port — and then sit proud of the face, because the extra thickness has nowhere to go.

This is the most expensive mistake in flange assembly, and it is invisible on a bench. Mark the class on the flange and on the port and check it before the bolts go in. ISO 6162-1 covers the 3000 psi class and ISO 6162-2 the 6000 psi class, and the same naming confusion runs through JIC vs SAE naming.

Why Four Bolts Instead of One Thread

A threaded port at two inch bore needs a very large hex and a very high tightening torque, and the resulting joint is sensitive to vibration loosening. A four-bolt flange spreads the same preload over a wide bolt circle, which resists loosening and allows much larger bore sizes at high flow. The split clamp also means the hose can be removed sideways without disturbing the port flange or the adjacent piping.

Assembly sequence matters more than the torque figure. Lubricate the O-ring with system fluid, seat the head square to the face, fit both clamp halves so the gap is even, then tighten in a cross pattern in two stages. A clamp tightened on one side first will cock the head and pinch the O-ring.

Weld-On, Crimp-On and Bolt-On Heads

The head can be attached to the circuit three ways. A crimp-on flange is assembled onto hose with a ferrule, exactly like any other hose fitting, and is the normal choice for flexible lines. A weld-on flange is welded to a tube or pipe and is used where a rigid line runs to the equipment. A bolt-on or threaded flange adapts an existing threaded port to a flange face.

The pressure class applies to all three. A weld-on Code 61 head on a tube that will see 5000 psi is a design error that no amount of weld quality will fix. If the line is rigid and the pressure is high, the tubing wall and the flange class have to be checked together. The other hose-end connections in our hydraulic fittings range follow the same rule.

Flat Face, O-Ring Groove and the Mistake at Assembly

Depending on the standard, the O-ring groove is machined either in the port flange or in the hose flange — never in both, and never in neither. Before assembly, look at the two faces: one should carry a groove with an O-ring in it, the other should be flat. Two flat faces will not seal. Two grooves will not seat.

The same check catches a wrong-class flange, because the groove depth differs between Code 61 and Code 62. A flat face also has no tolerance for grit: a single metal chip on the face creates a leak path that no bolt torque will close, which is why field repairs on flanges should include wiping both faces and fitting a new O-ring.

87311 SAE Flange 3000 PSI (ISO 12151-3 / SAE J516) — Standard Dimensions

Dimensions in mm. C is the flange head diameter, D the bore, L the flange thickness.

Code 61 vs Code 62 — What Actually Differs

The identical bolt pattern is the trap: both classes will assemble, and only one will hold pressure.

Frequently Asked Questions

What is the difference between Code 61 and Code 62 flanges?

Both are SAE J518 flange connections with the same bolt pattern for a given size, but Code 61 is rated to 3000 psi and Code 62 to 6000 psi. The Code 62 head is thicker and its O-ring groove is different. They look interchangeable and will bolt together, which is exactly why mixing them causes failures.

Can I use a Code 62 flange on a Code 61 port?

No. The bolt pattern matches, so it will assemble, but the thicker Code 62 head will not seat against the port face and the joint will leak or blow out under pressure. Always match the class of the head, the clamp and the port.

Do you supply split flange clamps and bolts?

Yes — split clamp kits in one-piece and two-piece designs, with or without bolts, for both Code 61 and Code 62 sizes. Specify the nominal size and the class when ordering, because the clamp must match the head thickness as well as the diameter.

Are stainless steel flanges available?

Yes, in 316L for marine, offshore and chemical applications. Stainless flange heads are usually supplied as weld-on or bolt-on rather than crimp-on, because the hose end is normally carbon steel with a stainless wetted path.

Why Choose HGW Flanges Fittings?

When it comes to flanges fittings, HGW Hydraulic stands out as a leader. Established in 1996, we bring 28 years of expertise to the table, crafting high-quality hydraulic solutions for industries like engineering, mining, and shipbuilding. Our flanges fittings, certified under ISO 14001:2015, are forged from durable stainless steel, ensuring exceptional strength and corrosion resistance. Need reliable connections for high-pressure systems? HGW offers customized options, including NPT, JIC, and metric styles, designed to meet your specific demands. With a proven track record and a commitment to excellence, HGW Hydraulic delivers flanges fittings that guarantee performance and longevity—making us the smart choice for your hydraulic needs!

How to Choose the Right Flanges Fittings?

Selecting the best flanges fittings doesn’t have to be daunting—HGW Hydraulic simplifies the process with these key steps:

1. Identify Your Connection: Match your system with NPT, JIC, or metric flanges fittings for seamless integration.
2. Assess Environmental Needs: Our stainless steel flanges fittings excel in harsh conditions, from mining rigs to marine applications.
3. Pick the Perfect Fit: Whether it’s a standard flange or a custom design, we tailor solutions to your specifications.
4. Lean on Expertise: Backed by 28 years of experience and ISO 14001:2015 certification, we ensure top-tier quality. Let HGW Hydraulic guide you to the right flanges fittings—contact us today for durable, precision-engineered solutions that keep your systems running smoothly!