Identifying fittings on imported machinery

What to expect by origin

European machinery is mostly metric 24 degree cone to DIN 2353 and ISO 8434-1, with BSPP ports on components sourced from Britain and Italy. British and Australian machinery is heavily BSPP and BSPT.

Japanese machinery runs JIS 30 degree flare on BSPP threads, and Komatsu and several others use a 30 degree flare on a metric thread instead. Those two have the same seat and completely different threads, so the seat alone will not separate them.

North American machinery is JIC, SAE O-ring boss, ORFS and NPT, which is the set most of this site's readers already know.

• Germany, Italy, Scandinavia: metric 24 degree cone, light and heavy series, plus BSPP ports.
• Britain, Australia: BSPP and BSPT, with JIC on hose ends.
• Japan: JIS 30 degree on BSPP threads; Komatsu 30 degree on metric threads.
• Korea, China: any of the above, frequently more than one on the same machine.

The three that catch people

First, NPT against BSPT. Both are tapered, both look identical at arm's length, and at 1/2 and 3/4 in trade size they share a thread count of 14 per inch with basic diameters 0.39 mm and 0.23 mm apart. An NPT male will start and pull up in an Rc female at those sizes. The flanks are 60 degrees against 55, so the joint bears on the crests and never wedges.

Second, NPT against BSPP. One is tapered and seals on the thread; the other is parallel and cannot. An NPT male wound into a BSPP port jams on the taper, feels tight, leaks, and bells the port out from the inside.

Third, JIS 30 degree against a plain BSPP. The JIS thread IS a BSPP thread - one guide states its dimensions are the same as BSPP - so a thread gauge will call it BSPP and be right. The 30 degree female cone is the only thing that tells them apart, and a plain BSPP male with a bonded washer will screw into a JIS swivel and seal against nothing.

Metric 24 degree: measure the tube, not the thread

The metric 24 degree cone is the most common connection on European machinery and the easiest to order wrong, because the thread does not identify the fitting.

Seven threads in DIN 2353 carry one tube diameter in the light series and a different one in the heavy series. M18 x 1.5 is 12 mm tube in light and 10 mm tube in heavy. All four identification sources agree on the map, and all four print it as two separate tables for exactly this reason.

The cutting ring is bored for one tube diameter. On the wrong one it will not bite properly and the joint blows the tube out under pressure, so measure the tube as well as the thread every time. The pressure ratings are far apart too - the light series runs in the low hundreds of bar where the heavy series reaches 630.

Japanese connections

JIS 30 degree flare uses BSPP threads and a 30 degree cone, normally on a loose female swivel nut. Komatsu style uses a 30 degree cone on a straight metric thread instead. They share a seat and share nothing else, and neither will start on the other.

The two identification guides this site cites agree on seven Komatsu threads - M18, M22, M24, M30, M33, M36 and M42, all at 1.5 mm pitch. They disagree about which tube M18 and M22 serve, so this site publishes no tube size for those two. One guide carries an M14 x 1.5 that the other does not, so that size is not published either.

The practical check is the thread form. A JIS fitting gauges as 55 degree Whitworth; a Komatsu fitting gauges as 60 degree metric. A 55 degree blade rocks on the Komatsu and a 60 degree blade rocks on the JIS.

What to do at the counter

Take the fitting, not a photograph, and take the tube diameter with it if the connection is metric. Give the counter the four readings - diameter, thread count, parallel or tapered, and the seat - rather than a family name you are guessing at.

If the machine is on a job and the fitting cannot come off, the seat and the thread count are both readable in place with a gauge and a torch, and between them they narrow most connections to one candidate.