Cam couplings, usually called camlocks, are the fastest way to join two hoses or connect a hose to a pump. There are no threads to line up and no tools involved. Push the two halves together, flip down two arms, and the joint is made.
The difficulty is the naming. Camlocks are sold as Part A, Part B, Part C and so on, and the letters give no clue as to what each one does. Order the wrong letter and you end up with two halves that physically cannot connect.
This guide explains what each letter means, how to work out which combination you need, and the sizing mistake that catches people out most often.
Key Takeaways
- Every camlock connection needs two halves: one female coupler and one male adaptor.
- The letter tells you two things: whether the cam side is male or female, and whether the other end is a hose tail or a BSP thread.
- Part C and Part E are the standard pair for joining hose to hose.
- Size the fitting to the internal bore of the hose, not to the pump outlet.
- Camlocks are interchangeable between manufacturers because they are made to published standards, principally BS EN 14420-7 in the UK.
- Camlocks are a quick release fitting. They are not suitable for steam, and not intended for permanent or concealed pipework.
What is a camlock fitting?
A camlock is a two part hose coupling. The female half, called a coupler, has a socket with two hinged arms. The male half, called an adaptor, has a smooth spigot with a groove machined around it.
When you push the adaptor into the coupler and rotate the arms down, cams on the inside of the arms engage that groove and pull the two halves tightly together. The seal is made by a gasket that sits inside the face of the coupler. The arms lock over centre, so they will not spring open on their own.
That design is why camlocks are so widely used in dewatering, site pumping, agriculture and tanker transfer. A connection that would take a minute with threaded fittings and a spanner takes a couple of seconds by hand, which matters when a pump is being moved repeatedly through a shift.
What do the camlock letters mean?
The lettering comes from the standards that govern these fittings. Once you know the logic it is straightforward: each letter is a combination of one cam end and one connection end.
The four parts most people need
These four cover the majority of pump and hose work.
| Part | Cam end | Other end | What it does |
|---|---|---|---|
| Part A | Male adaptor | Female BSP thread | Screws onto a male threaded pump outlet. Accepts a Part C. |
| Part C | Female coupler | Hose tail | Clamps onto the hose. Accepts a Part A or a Part E. |
| Part D | Female coupler | Female BSP thread | Screws onto a male threaded pump outlet. Accepts a Part E. |
| Part E | Male adaptor | Hose tail | Clamps onto the hose. Pushes into a Part C or a Part D. |
You can browse all four in our range: Part A cam adaptor, Part C cam coupling, Part D cam coupling and Part E cam adaptor.
Which combination do I need?
Work backwards from what is at each end of the connection.
Connecting a hose to a threaded pump outlet
Most pump outlets have a male BSP thread. You need a fitting that screws over that thread and presents a cam end, then a matching cam fitting clamped onto the hose.
- Part A on the pump, Part C on the hose, or
- Part D on the pump, Part E on the hose
Both arrangements work equally well. The important thing is to choose one and use it consistently, so that any hose you own fits any pump you own.
If your pump has a female threaded outlet instead, you need a Part B or Part F on the pump.
Joining hose to hose
This is the classic pairing:
Hose → Part C ⇆ Part E → Hose
The Part C carries the arms and the gasket. The Part E is the spigot that locks into it.
Building a set of extension hoses
If you fit Part E at the inlet and Part C at the outlet of every extension hose, you can daisy chain as many lengths as you need, in any order:
Pump → A → C → hose → E ⇆ C → extension → E ⇆ C → extension
For long runs, remember that flow reduces as distance and lift increase. Our guide on how far a water pump can move water explains how to work out what you will actually achieve.
Sizing: match the hose, not the pump
This is where most wrong orders happen. Camlock sizes refer to the nominal internal bore of the hose, not to the pump outlet thread. A 50mm Part C is designed to clamp onto 50mm (2 inch) hose.
Two rules follow from that:
- Camlocks only mate with the same nominal size. A 50mm coupler will not accept a 25mm adaptor, even though both are camlocks.
- Any change of size has to happen at the threaded end, before the cam fitting. There is no reducing camlock.
If your pump outlet and your hose are different sizes, read our guide on whether you can reduce the hose size on your pump first, because reducing a discharge line has consequences for flow and pressure.
Camlocks are also available for suction and delivery hose and layflat discharge hose in the same size range.
What makes the parts interchangeable?
Camlocks made by different manufacturers generally fit each other, and that is not a coincidence. It is the result of two published specifications.
The original standard was the US military specification MIL-C-27487, which set out dimensions, tolerances, materials and pressure ratings, and was replaced in 1998 by the US federal specification A-A-59326. Compliance with that specification is what guarantees that a coupler from one maker accepts an adaptor from another.
In the UK and Europe, the relevant standard is BS EN 14420-7:2022, Hose fittings with clamp units, Part 7: Cam locking couplings, published by BSI as the UK implementation of EN 14420-7:2022. It specifies the design, materials, dimensions and marking requirements for cam locking couplings used to transfer liquids, solids and gases.
That standard sets a working pressure range of -0.8 bar to 16 bar for couplings within its scope, with cast aluminium couplings and larger DN 100 sizes limited to -0.8 bar to 10 bar. The standard working temperature range for a nitrile (NBR) main gasket is -20°C to +65°C.
Where camlocks should not be used
Camlocks are excellent at what they do, but they are a quick release fitting, and the scope of the standard makes the limits clear.
- Not for steam. BS EN 14420-7 explicitly excludes steam and liquefied gas from its scope.
- Not for compressed air. Industry guidance advises against it, because a coupling that releases under pressure is a safety risk.
- Not for permanent or concealed pipework. These are fittings you expect to inspect and reconnect.
- Not for mixing materials. Pairing an aluminium half with a polypropylene half is not recommended, as the two do not deform equally under clamping load.
- Check gasket compatibility before using them for anything other than water. The gasket, not the body, usually determines chemical and temperature suitability.
Fitting and maintenance
- Push the hose tail fully into the hose so that every barb sits inside the bore. Warming the hose end in warm water helps on a tight fit.
- Always secure the tail with a hose clip or a hose clamp. A hose tail is not self retaining.
- Wipe the gasket and the mating face before every connection. Grit on the gasket is the most common cause of a leaking cam joint.
- Close both arms every time. One arm will feel as though it is holding, and under flow it will not be.
- On the suction side, a joint that draws air will stop a pump priming even when nothing looks wet. Check the gasket first.
- Replace gaskets when they harden, flatten or split. They are a wearing part.
Why this matters for flood and water management
Quick release couplings are not just a convenience. According to the Environment Agency's National Flood Risk Assessment, published in December 2024, around 6.3 million properties in England are in areas at risk of flooding from rivers, the sea or surface water, and around 4.6 million of those are at risk from surface water flooding specifically. The Environment Agency notes this represents a 43% increase on its previous assessment, largely because of improved data and modelling.
Surface water flooding is fast moving and unpredictable. When a response depends on getting a pump running and a discharge line laid quickly, sometimes in poor light and cold conditions, a connection that can be made and remade by hand is a practical advantage over one that needs a spanner.
Conclusion
The lettering looks arbitrary but the logic is simple. Every camlock joint needs one female coupler and one male adaptor of the same nominal size, and the letter tells you which you are holding and what is on the back of it.
For most pump work, remember three things. Part C and Part E join hose to hose. Part A or Part D gets you from a threaded pump outlet to a cam connection. And size the fitting to the hose bore, not the pump outlet.
