SAE Flanges

The SAE split-flange connection gives each of a joint's two jobs its own hardware: an O-ring set in a groove on the flange head seals against a flat, unthreaded port face, while four cap screws carry the separating load. Nothing threads into the port, so there is no thread to gall or seize — but clamp load comes from the bolts alone, and they must be pulled down evenly.

The arrangement earns its place as bore grows, where a thread wants a wrench flat nobody can reach. SAE J518 fixes the pattern in two classes: Code 61 standard pressure, Code 62 high pressure. Nominal sizes overlap, but a Code 62 head is thicker on a wider bolt circle, so the classes will not mate and must never be mixed. The cost is four fasteners and room to turn them.

Where it's specified

• Pump and motor ports — a cast housing carries a machined flat and four tapped holes more easily than a deep thread
• Large-bore suction and return — from about 1/2" to 5" the flange stays compact where a thread turns unwieldy
• High-pressure circuits — Code 62 puts more clamp load behind the seal
• Joints opened for service — only the O-ring is disturbed, so the port face survives

Range and materials. Flange heads, split and captive clamps, straight, 45° and 90° elbows, blocks, weld-on halves, covers and bolt kits cover Code 61 and Code 62 from about 1/2" to 5" in carbon steel and stainless, nitrile O-rings standard. Threaded adapters take a flange head to JIC 37°, ORFS, NPT, BSP or O-ring boss.

Ordering notes. Identify the class before the size: measure bolt circle and head thickness rather than nominal bore, since the classes look alike in a bin. Draw the screws down in a cross pattern in stages to the manufacturer's figure: pulling one corner home first cocks the head and pinches the O-ring, leaving a weep more torque cannot cure.