SAE J1926 / ISO 11926 ORB Port Dimensions Chart & Calculator

How Does an SAE J1926 / ISO 11926 O-Ring Boss Port Seal High Pressure?

Tapered pipe threads such as NPT and BSPT seal by metal-to-metal flank wedging, which frequently splits thin aluminum valve bodies and introduces shredded PTFE tape into sensitive proportional spools. To eliminate leakage in high-pressure hydraulic manifolds up to 630 bar (9,137 psi), ISO 11926-1 (SAE O-Ring Boss Ports) and SAE J1926-1 separate the mechanical retention function from the fluid sealing function. Straight Class 2B threads governed by ASME B1.1 (Unified Screw Threads) resist the axial hydraulic ejection load, while a 90 Shore A durometer elastomer O-ring from the AS568-900 series sits trapped inside a truncated conical chamfer at the mouth of the port, backed up by the fitting's hex face or a captive steel washer against a flat spotface.

Machining a leak-free SAE ORB cavity requires holding five concentric dimensions—typically plunged in a single pass with a carbide port-contour form tool before tapping or thread milling: the minimum spotface diameter d3 (perpendicular within 0.15°), the seal chamfer entrance diameter d4 (held to +0.13/−0.00 mm), the chamfer depth L1, the conical angle (12° ± 1° for dash sizes -02 through -10, and 15° ± 1° for -12 through -20), and the minimum full thread depth L2. Engineering catalogs from Parker Hannifin Tube Fittings Division (Catalog 4300) and Brennan Industries emphasize that the seal chamfer wall roughness must not exceed 63 µin R_a (1.6 µm), with zero radial chatter marks.

Why Do Dash Sizes -12 and Larger Switch to 12-UN Threads and a 15° Chamfer?

In the smaller dash sizes -02 through -10, SAE J1926 uses the standard Unified Fine (UNF) series—ranging from 5/16-24 UNF on a -02 port up to 7/8-14 UNF on a -10 port—paired with thinner O-ring cross-sections (1.63 to 2.46 mm) that compress optimally inside a steep 12° taper. Starting at dash size -12 (3/4 in tube OD, 1-1/16-12 UN-2B), continuing with coarse or standard UNF pitches would require excessive installation wrench torque and deep tap engagement. Therefore, sizes -12, -16, and -20 standardize on the constant-pitch 12-UN-2B series defined in Machinery's Handbook (31st Ed., Industrial Press) and open the seal chamfer to 15° to accommodate the thicker 2.95 mm and 3.00 mm O-ring cross-sections without overfilling the gland volume.

Worked Examples: Steel vs. Aluminum Manifold Pressure Derating

Worked Example 1 (SAE -08 in Steel vs. 6061-T6 Aluminum): For an SAE -08 port in carbon or alloy steel, our calculator returns a 3/4-16 UNF-2B thread (pre-tap drill 17.5 mm / 0.689 in), a 12° seal chamfer of entrance diameter d4 = 20.60 mm (0.811 in) by depth L1 = 2.4 mm, spotface d3 = 30.0 mm, and full thread depth L2 = 14.3 mm. With an AS568-908 O-ring (90 Shore A) torqued to 80 N·m (59.0 ft·lb) (converted via NIST Special Publication 811), the steel port is rated to 420 bar (6,092 psi). In a 6061-T6 aluminum manifold (tensile properties per ISO 6892-1 (Metallic Tensile Testing)), working pressure derates by 45% to 252 bar (3,655 psi) at a reduced torque of 52 N·m (38.4 ft·lb).

Worked Example 2 (SAE -12 Heavy Return Port): For an SAE -12 port (1-1/16-12 UN-2B, pre-tap drill 24.8 mm), the 15° chamfer measures 29.15 × 3.2 mm with an AS568-912 O-ring rated to 420 bar (6,092 psi) at 180 N·m. Compare tapered ports on our NPT pipe tap drill chart and BSPP/BSPT British pipe chart, size face seals on the AS568 O-ring groove chart, or program the port threads with our CNC thread milling calculator.