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Gas Threads Explained In Plain English.

Article by Peter Smith - Caravans Plus
Read Time: 4 mins

How to measure the gas/water fittings you need

Gas fittings and hoses used in Australian Caravans and Motorhomes use a number of different threads. They may seem hard at first, but a short read will give you enough information to purchase the correct part.

The following information is educational and general in nature only. Licensed Gas Fitters are required to install gas fittings into RVs.

All gas components on this website that have threads also have a list of other components that will connect to them. They are listed below each product description. This feature allows you to ensure all components from gas cylinder to gas appliance are compatible.

1) BSP (British Standard Pipe)

BSP threads are the most common and can be used for gas and water. The sizes are imperial.

To get a 100% seal with gas you use a yellow thread or Liquid thread seal. You can use white or yellow for water.

When used for water the most common one you will know around the home is on your garden tap. Most garden hose fittings come with a 3/4" BSP to 1" BSP adapter.

Gas Threads Explained

The size quoted for threads is indicative of the internal bore size, not the diameter of the thread.

Gas Threads Explained

Click here to print a Thread Sight Guide to lay your thread on.

Click to display an actual size thread template

Above: If you have an existing thread that looks like those above, you need to measure the outside of the male thread as shown. The male thread is generally tapered so that it gets tighter when screwed in.

9.5mm measured OD is Male BSP 1/8"
13mm measured OD is Male BSP 1/4"
16mm measured OD is Male BSP 3/8"
21mm measured OD is Male BSP 1/2"
26mm measured OD is Male BSP 3/4"
37mm measured OD is Male BSP 1"

Above: If it is a female fitting, measure the inside to determine the actual name. Measured sizes are shown as approx. mm

8mm measured ID is Female BSP 1/8"
11mm measured ID is Female BSP 1/4"
14mm measured ID is Female BSP 3/8"
17mm measured ID is Female BSP 1/2"
21mm measured ID is Female BSP 3/4"
31mm measured ID is Female BSP 1"

2) SAE 45 degree flare

The male fittings are easily identified by the 45 degree flare at the end. These screw into either a SAE nut on the end of a copper pipe or a gas hose.

When used with copper pipe, the pipe is flared to 45 degree. The nut will not fall off and the copper section creates the seal between the nut and SAE 45 flare brass fitting. No thread tape is required with these fittings.

Gas Threads Explained

The Outside Diameter of the thread can be measured to give you the correct name of the fitting.

11mm measured OD is Male SAE 1/4"
13mm measured OD is Male SAE 5/16"
16mm measured OD is Male SAE 3/8"

Measure the Inside Diameter to get the correct name of the nut. The nuts always swivel. They have an inverted flare inside.

10mm measured ID is Female SAE 1/4"
11mm measured ID is Female SAE 5/16"
14mm measured ID is Female SAE 3/8"

The nut shown is a 5/16" nut because it fits on a 5/16" pipe.

The recommended pipe dia. for a typical gas installation within a Caravan or Motorhome is 5/16" copper pipe.

If you have a gas BBQ, Gas stove, Gas HWS, Gas heater and large Gas fridge - you may need 3/8" pipe, but your gas fitter can determine this.

3) POL fittings

Used on larger gas cylinders these have a Left Hand thread. Many male fittings have a rubber o-ring and must not be over tightened.

Gas Threads Explained

4) Primus gas cylinder threads

One notable difference with this thread is that gas will only flow after the fitting is fully inserted into the cylinder.

Gas Threads Explained

5) 3/8 inch Left Hand gas cylinder threads

Often called Companion but used by other brands as well.

Gas Threads Explained

6) Bayonet fittings

Used for removable gas appliances. The female fitting is used to supply the gas and comes in one size only. A rubber cap should be placed on these if subject to dust or dirt.

caravan bayonet fittings

7) Inverted Flare 1/4

This is used at the end of gas pigtails that connect to a change-over value. The seal does NOT require thread tape.

Gas Threads Explained

Was this helpful?


  • comment-avatar


    Useful information but would be even more so if the thread pitches were also listed.

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    Very useful, always been confusing working out difference between gas,air and many other threads

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    Colombia vm tröja

    Maintain the exceptional work !! Lovin' it!

  • comment-avatar


    Hi I own a Weber Baby Q and I have a camper trailer that has a female bayonet fitting. I would like to connect the Baby Q to that fitting so that I can use the on board gas facilities rather than carrying a separate gas bottle. Is there an adapter that has a female POL fitting on one end and a male bayonet fitting on the other? Thanks Nelson

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    The Weber range use a male 3/8 flare connection, not a POL. The POL is the fitting used on a gas bottle. What you need is a male bayonet to female 3/8. Search on the web there are plenty available.

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    Can't ask anything better. I felt like I went for a crash course on gas fittings. I really appreciate the time these people spend to make this website and anyone understand about gas adapters on how to measure it and

  • comment-avatar


    This is the best Web page I have recently searched on Internet. I really appreciate the time these people took make it simple for anyone to understand about gas fittings. It was a crash course and can't ask for anything better. Great work.

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    Is it not time that the intrepid Australian Government set about standardising the type of threads etc of, not just these, but all fittings. I know it will take years to implement, but it will help save the sanity of generations of Aussies to come.

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    That's fanciful as the planet is obsessed with variety for variety's sake. Take the horrible case of electronics 'they " promised to standardize semiconductors after the valve era, then ics after transistors and so on. The result? even more diversification. I have come to believe its due to 2 things 1. a need to "make ones mark" and 2. a need to capture a market buy being a sort of gatekeeper on specs.

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    How about typical water containers that have a 20mm threaded hole? Can I fit a 3/4" BSP in that?

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    The 20 litre water jerrycans we sell definitely take a 3/4 BSP fitting, usually a tap

  • comment-avatar

    Thomas Thrasher

    Hello, great table and explanation. My question is will a 3/8" SAE male fit properly in a 3/8" BSP female? I have a quick connect that has a 3/8" SAE male and I want to know if I can mate it with a 3/8" BSP gas hose for BBQ.

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    Peter - CaravansPlus

    SAE and BSP cannot directly connect. You must use one or more connectors. Some single connectors have BSP and SAE but more often than not you will need more than one connector to achieve the correct male/female option or size. Use the "Connecting products" button at the bottom of any fitting that has 3/8 SAE male thread to get started.

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    (37mm measured OD is Male BSP 1")-That is incorrect. 33mm measured OD is Male BSP 1"

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    Question I have what is the size and type of tread of the actual gas jet is it 7/32" fine ? I know its not metric.

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    As usual very useful thanks. Just needs to add the NPT thread as it is used on regulators and hoses.

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    Sooooo, if we just use normal measures across 1.6 cms not 21 mms the diameter of the components why are they not matching the ruler or each other?? 1/2 inch is closer to 1,7cm NOT 21 mm. one chart says 13mm measured OD is Male SAE 5/16" but then the OTHER says 13mm measured OD is Male BSP 1/4"???? The measures fluctuate??

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