How To Check If My Old Hydraulic Coupler Fits Iso7241 Series A Or B?

2026-07-02

If you've ever stood in your workshop holding an old Hydraulic Coupler, wondering whether it'sISO 7241-1 Series Aor Series B, you're not alone. I've been there too—staring at a worn-out Quick Coupling, trying to figure out which replacement to order so I don't end up with something that doesn't fit.

How to check if hydraulic coupler fits ISO 7241 Series A or B - measuring male tip diameter to identify quick coupling type.png

Here's the thing: ISO 7241-1 Series A and Series B are NOT interchangeable. They look similar at first glance, but they're built to different dimensional standards. Pop a Series A male into a Series B female, and you'll get nothing but frustration (and probably a leak).

So how do you check which one you've got? Here are a few practical ways.

Look for markings on the coupler body

Many manufacturers stamp the standard right on the coupling. You might see "ISO A," "ISO 7241-1A," or something like "6600 Series" (which is Parker's ISO A line). If you spot "60 Series" or "FD45," that's typically ISO B territory. Not all couplers have clear markings, though—especially older ones—so don't rely on this alone.

Measure the male tip diameter

This is the most reliable method. Grab a caliper and measure the first step of the male coupler (the nose section). According to the ISO 7241-1 standard

Body Size	ISO A Diameter (mm)	ISO B Diameter (mm)
1/4″ (6.3)	11.73–11.86	14.1–14.2
3/8″ (10)	17.2–17.3	19–19.1
1/2″ (12.5)	20.48–20.56	23.44–23.55
3/4″ (19)	29–29.1	31.34–31.45

If your measurement matches the left column, you've got Series A. If it matches the right, you're looking at Series B.

Consider where your equipment came from

This isn't foolproof, but it's a solid clue. ISO 7241-1 Series A is used predominantly in Europe and is the preferred choice worldwide for agricultural and forestry machinery. Series B is more common in North America and shows up a lot in industrial and chemical applications. If your machine was built in Europe, chances are it runs on Series A. American-made? Probably Series B.

Why does this matter?

Getting it wrong means wasted time, money, and potentially unsafe connections. At Hejian Honglun Hydraulic Parts Co., Ltd., we've been manufacturing hydraulic Quick Couplings since 2010, and we see this confusion all the time. Our HL brand quick couplings conform toISO 7241-1 Series A, ISO 7241-1 Series B, ISO 5675, ISO 16028, and Chinese standards. They interchange with major brands like Parker, Faster, Aeroquip, Hansen, Nitto, Foster, Cejn, and Rectus—with quality that stands up to those international names.

We export to more than 30 countries, including the US, UK, Germany, Spain, Italy, Russia, and across Southeast Asia. Whether you need ISO A, ISO B, or something else, we've got you covered.

Still not sure which one you need?

Drop us a message with a photo or measurement of your old coupler—we'll help you figure it out. Visit https://www.hlfluid.com/products/ to browse our full range, or reach out directly at sales@hlfluid.com.

Don't guess. Get the right fit the first time.