JIS Square Flanges

It joins pipe to pipe, or pipe to a component, inside a hydraulic system. The body is square, four bolts pass through the corners, and an O-ring in a machined groove does the sealing rather than metal-to-metal contact. It gives a compact high-pressure joint that can be broken and remade without disturbing the pipe run.

Two separate standards. JIS B2291 is the hydraulic square flange standard — machinery, presses and plant; our 210K SHA/SHB range is marked to it. JIS F7806 is the shipbuilding standard, written for piping onboard ships and offshore structures — it covers the 280K and 350K KA/KB ranges. Dimensions and pressure series differ; halves are not interchangeable between them. Where the flanges go into equipment essential to the ship’s safety or propulsion, confirmation from the classification society is still required.

The nominal working pressure in kgf/cm² — the legacy label the trade still orders by. The rating the standards state is a round SI figure: 21 MPa (210 bar), 28 MPa (280 bar), 35 MPa (350 bar). So a drawing asking for a hard 21 MPa is met by 210K — do not convert the kgf/cm² label and talk yourself into the next series up.

A is the O-ring side — the half carrying the machined groove (our catalogue also calls it the counter-flange). B is the flat side. The two are handed and ordered as a pair — two of the same letter will not seal. SH, SS, K and LS denote the type family, which goes with the pressure series and the standard.

No. The bolt-hole centres differ between series at almost every size — at 25A: 53, 58 and 65 mm for 210K, 280K, 350K — so the bolts will not line up, and the O-ring groove differs too. The exception is 100A, where 210K and 280K share the same 140 mm pitch and 190 mm body, so they can be bolted up by mistake — separate them by thickness (C = 55 mm in 210K, 65 mm in 280K) or by the marking. Getting it wrong puts a 210 bar flange in a 280 bar line.

No, in no size. An SAE J518 flange is round-bodied, rated in psi classes (Code 61/62), dimensioned in inches. A JIS square flange is square-bodied, rated in kgf/cm², dimensioned in millimetres. The bolt patterns, ports and O-rings are all different. We stock both lines — tell us which one the existing installation uses.

NBR HS90 to JIS B2401-1B, in the G series for most sizes (the P series at 15A in the higher pressure ranges). The size is fixed by the flange and differs across the series: 50A takes G60 in 210K, G55 in 280K, G50 in 350K. Replace the O-ring every time the joint is broken. Viton (FKM) is available where the fluid or temperature rules out nitrile.

SF440A, a forged carbon steel to JIS G3201 — the same grade across all three pressure series; the higher series carry more pressure through heavier sections and larger bolts, not a different steel. SS316 is available in any series for deck, splash-zone, chemical or washdown service. In ASTM terms SF440A sits with the SA-105 grades.

Yes — 1/4″ to 6″ across all three series, as complete sets (A half, B half, O-ring, four bolts, four nuts), held in our regional warehouses in Singapore and Malaysia. Goods leave the warehouse within 24 hours of your PO, with the delivery schedule to your city confirmed in the quotation. An EN 10204 3.1 certificate follows the forging.

State seven things: the size (1/4–6″ or the A size); the series (210K/280K/350K); the type letter (SHA/SHB, SSA/SSB, KA/KB, LSA); weld-in or blind; the material (SF440A/SS316); the pipe schedule (SCH 40/80/160 — at 32A in the 210K series the schedule also changes the O-ring); and the application (B2291 or F7806). Send it via WhatsApp ★ Google reviews ▶ YouTube channel or the contact form — a quote comes back within 2 working hours.