International Couplings

International Coupling Identification

The generic term "metrics" has been applied to most non-North American thread ends. A more correct description is "international thread ends." International thread ends can be metric, measured in millimeters, but they can also include BSP (British Standard Pipe) threads which are measured in inches.

Here are the two basic categories. Those in the first column are measured in millimeters, those in the second column in inches.

Metric Threads British Threads
Very Fine BSPT
Fine JIS
GAZ - Fine  
Komatsu - Fine  

Knowing the country of origin for a piece of equipment will give you your first clue as to what type of thread end is used. If it is a German or Swedish manufacturer, it is probably a DIN (Deutsch Industrial Norme) fitting. If it is English, it is most likely BSP. Japanese Komatsu equipment uses the Komatsu fitting (with metric threads). Other Japanese equipment most likely will be JIS (Japanese Industrial Standard), or in some cases, BSP, straight or tapered threads.

Great Britain

Great Britain BSPP (British Standard Pipe Parallel)

BSP is the most popular thread end in Great Britain. These threads are either parallel (BSPP) or tapered (BSPT). The male BSPP will mate with a BSPP (parallel female or a female port). The male BSPT will mate with the BSPP female swivel. The male has straight threads and a 30-degree inverted seat. The BSPP female has straight threads and a 30-degree inverted seat. The female port has straight threads and spotface. The seal on the port is made with an "O" Ring or a soft metal washer on the male. The BSPP connector is similar to, but not interchangeable with our FPX. The thread pitch is different in most sizes, and the thread angle is 55-degrees instead of the 60-degree angle found on NPSM threads.

BSPT (British Standard Pipe Tapered)

The BSPT (tapered) male will mate with a BSPT (tapered) female and the BSPP female swivel. The BSPT male has tapered threads and a 30-degree inverted seat. The BSPT connector is similar to but not interchangeable with our MP. The thread pitch is different in most cases, and the thread angle is 55 degrees instead of the 60-degree angle found on NPTF threads. Neither the British parallel pipe or the British tapered pipe has true metric threads, although many people find these threads "foreign" and conclude they must be "metric."


DIN is the most common "metric fitting, with threads and an inverted flare (either 12 degrees or 30 degrees) The male has a recessed counterbore which matches the Tube O.D. of the coupling used with it. The mating female is one of these:

  • A Universal, or globe, seal (12 degrees/30 degrees inverted cone.)
  • A 12 degree inverted cone with an "O" Ring.
  • A metric tube fitting

DIN fittings are available in both Light and Heavy Series. The Heavy Series is normally found on high-pressure lines and the female usually has an O-Ring seal on the cone. The O-Ring can also be found on lower pressure lines, but it is not a necessity.

The standpipe fitting is also fairly common. It is a coupling stem with machined tubing on the end instead of threads. It is used with a metric nut and sleeve to mate with the same metric connectors as the swivels. The size is determined by measuring the O.D. of the standpipe or tube. A female swivel coupling often can be used instead of a standpipe assembly. A male metric (MM) adapter normally is used for DIN 3852 port connections. It has an O-Ring and retaining ring for sealing.

To correctly identify the DIN fitting size measure the following:

  • Using a thread gauge, determine the number of millimeters per thread.
  • With calipers, find the thread diameter by measuring the O.D. on the male and I.D. on the female.
  • Measure the Tube O.D. with the calipers so you can identify the fitting as either light Series or Heavy Series.

Identifying the female swivel can be difficult. The simplest and most accurate way is to use a Gates Female Thread Identification Kit (Prod No. 7369-0319), which contains male "plugs" of the most popular BSP and metric threads. Using this kit involves simply coupling the female fitting to the male plug of a known size to correctly identify the female threads. Then, the Tube O.D. is measured to determine if it is a Light Series or Heavy Series DIN.

Flanges are equivalent to SAE Code 61. However the bolts are metric. Metric bolts (except -20 size) have larger thread O.D. than SAE bolts. If using SAE flange halves, the bolt holes will need to be enlarged. Since the -20 metric bolt is smaller than the SAE bolt, a metric flange half should be used to assure proper fit.


The three most popular coupling styles from Japan are:

Japanese Industrial Standard: This coupling looks similar to our MJ and FJX fittings. There are two major differences - the threads are BSP and the seat angle is only 30-degrees instead of 37-degrees.

Komatsu: This fitting looks similar to the JIS fitting. The major difference: Metric Threads, not BSP.

Japanese Tapered Pipe Thread: This connector has the same thread as BSPT and will mate with BSPT connectors. It will NOT mate with the BSPP female swivel because it lacks the 30 degree inverted seat. Flanges for most Japanese hydraulic equipment - including Komatsu - are standard Codes 61 or 62 except for -10. Some drop dimensions are slightly different and the O-Ring dimensions are different. Be sure to use the SAE O-Ring in the SAE flange when replacing a Komatsu flange.

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