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Air tank adaptors

300 to 200 adaptor
A 300 bar to 200 bar high-pressure air adaptor.

This report covers:

  • Life was simple
  • History
  • 1/8-inch BSP thread
  • Adaptors
  • What to do?
  • Here they come to save the daaaaay!
  • Also bought the German adaptor
  • Not so fast
  • Why?

You are a dark-sider (a user of precharged pneumatic — PCP — airguns) or you want to become one. Your world is or will become one of adaptors, as we shall see today.

Life was simple

Though they are the last major airgun powerplant to come into being, spring-piston powerplants made things so simple that they soon dominated sales. With springers there is no compressed air to deal with. You don’t “charge” a springer, you cock it. When the trigger releases the piston the mainspring pushes it forward so fast that it compresses a small amount of air to get behind the pellet. That’s your power source.

Yes, springers are convenient, but if you want to shoot a lot of shots without doing much between each one, the PCP is the way to go.


We believe PCPs were first made sometime in the mid 16th century, perhaps around 1550 or so. There are no airguns from that time remaining, but a gun in the Royal Danish Museum that’s dated 1604 is too advanced to have been the first airgun. Something had to come before.

To fill those early air rifles each one had a dedicated hand pump that the air reservoir connected to. Because they were made by hand it was commonplace to connect the pump directly to the airgun’s reservoir. And the maker made everything, so the fit was his responsibility.

Fast-forward to 1980 when Daystate created the modern .22-caliber PCP. It changed the world. The Daystate Huntsman was a modern airgun in every sense of the word. It needed a convenient way to get high pressure air into its reservoir. But it wasn’t the Brits who first did this. Early PCPs from the UK were highly cabalistic. You had to be a member of their secret society to learn the well-guarded processes for introducing air into the reservoir of a PCP from the UK. There was very little standardization of fittings, fill pressures and even of devices that attached the airguns to scuba tanks.

Then came the Koreans with fill devices guaranteed to destroy the seals in their guns. A fill from zero to 3,000 psi took only seconds when you drove the fill “nail” into the fitting on the air tank. I wish I had a picture to show you, but that fill method came and went in a very brief time and I can’t find pictures anywhere.

1/8-inch BSP thread

I’m not going to discuss the threads that were found on fill hoses. They connect your air rifle to the adaptor found on the scuba tank. The most common was 1/8-inch British Standard Pipe (BSP) thread, not to be confused with 1/8-inch British Standard Pipe Parallel  (BSPP) that is today more common.

In the 1980s, ’90s and even into this century there wasn’t much commonality in the world of pneumatic fill hose thread patterns. Today it’s a little more standardized, but some countries or manufacturers still hold out for their different thread preferences.


I went though all of that to get to today’s subject — air tank adaptors. These are the devices that connect your fill hoses or the fill yokes those hoses come out of to your air tanks. Many high-pressure air tanks have threaded output holes that are rated in DIN standards. DIN is short for Deutsches Institut fur Normung eV — German Industrial Standard Institute. A 300-bar DIN thread pattern has a thread depth to safely handle pressurized air transfer at 300 bar, which is 4,350 psi.

There is a different DIN standard for the adaptor that connects to a scuba tank outlet. This one is rated to 200 bar which is 2900 psi, and, though it is the same diameter and thread count as the 300 bar adaptor, the two won’t interchange because each fails to seal in the other.

Tank adaptors
And here is the problem. The 200 bar DIN adaptor on the left will screw into a 300-bar DIN hole (adaptor shown on the right) and vice-versa but they won’t seal. 

When I wanted to fill my FWB P44 air pistol tank that has a 200-bar fill adaptor for the pistol’s reservoir, my only air sources are carbon fiber tanks that have 300 bar valves.  No el-fitto! Ironically, the last time I filled that pistol’s air tank I had a 3,000 psi scuba tank that had a 200 bar valve hole.

Build a Custom Airgun

What to do?

Obviously I needed a way to connect my large air carbon fiber tank to my pistol’s air reservoir. How frustrating to have what you need mere inches from where you need it with no way to get it there! Well, in my typical way of responding — I went ballistic! I wanted to shoot that pistol NOW! So I searched the internet and found a strange German website that had a 300 bar male to 200 bar female air adaptor. I bought it, but the strange German website wasn’t sure they had one or could even get one for me. Please leave your contact information and we’ll get back to you.

300 to 200 adaptor
German 300 bar to 200 bar adaptor.

Here they come to save the daaaaay!

Then I wondered whether Pyramyd AIR might have what I need. Sure enough, they did and I bought it. It was half the price of the German adaptor but it was purpose-built for the P44 reservoir. The P44 reservoir adaptor screws into this adaptor that has a Foster quick-disconnect fitting on the other end. Problem solved! But I just checked and it looks like I got the last one.

FWB 200 bar adaptor
Pyramyd AIR adaptor (top) for FWB P44 fill adaptor (bottom). The Foster fitting solves everything.

Also bought the German adaptor

I did also buy the German adaptor because it is universal, where the Pyramyd adaptor is specific to just one airgun. I never know with this blog what I’m going to connect to next.

Not so fast

Before you finish your coffee and go on about your business, consider this. While there are two bar thread patterns, there are four possible combinations for just this one adaptor. Male on both ends, female on both ends and male/female on either end. Better think about what you need.


Why am I telling you all of this? I’m telling you because the need for adaptors comes at the worst time — when you don’t have one that you need. This is my warning to you darksiders to plan ahead. I now have a drawer filled with adaptors that go from this to that. I know this report plays into the hands of the springer lovers, but guys, this is the reality of the game we play.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

32 thoughts on “Air tank adaptors”

  1. Tom,

    Just wondering if it is necessary to place something in between the threads to ensure a leak free connection? Or does the O-ring at the interface suffice?


    • Siraniko,

      That was (and always is) the first thing I tried when things didn’t work out. Doesn’t work with these big guys. 🙁


  2. HaHaHa,
    Serves them right. At least one per range session somebody comes in wanting to fill their tank or gun, without proper fittings and bleed valves and other miscellaneous filling doohickies. Why is there no standard? Does the UN need to pass a resolution to get UK, US, German, Czech, Slovenian, Russian, Slovakian, Korean, Chinese, Swiss, Swedish, Spanish, Austrian manufacturers all agree on a standard. Where is MCI when you need them???


    PS please add the remaining nationalities that manufacture PCP’s. I am sure I missed a few.

  3. Some times the universe conspires to get things done. I changed an adapter set recently and I could only fill to 200 bars. Never considered, of course, the possibility of a wrong part. After coffee I will start searching for the correct adapter. Sorry Shootski, Yogi must have a big smile on his face already if he reads this.

  4. I have been fortunate (un-) to only have bought American PCPs. They have standardized on the foster fitting with 1/8 BSP threading. One day when I grow up, I hope to have these difficulties.

    • FM be happy enough with his Maximi – might add a Marauder to the family down the road but the goal is to keep the fun at maximum level and the drama at minimum.

  5. BB,

    Seems that the Feinwerkbau target pistol reservoirs are designed to be filled directly off of the scuba tank (no hose). I had to get the same adapter as you did.

    Having several different brands of PCPs I’ve solved the unique fill probe problem by adding a foster QD connector (1/8 BSP to Foster ) to all the probes so it only takes a second snap the correct one on to the hose.


    Seems that the industry is aware that the lack of standardization is a problem but the design of the airgun requires special probe. Seen that some custom fill probes are now supplied with a Foster instead of the 1/8 BSP thread and that third-party manufacturers are also offering this solution.

    As RR pointed out, not all “Foster” fittings are compatible. Don’t know if it was an incorrectly made part or just an accumulation of tolerances but I’ve had one that wouldn’t seat properly. Shiny spots on the brass fitting showed the binding spot and a little polishing fixed the problem – that fitting is still a bit stiff but it seats and seals fine now.

    Guess that if someone who likes PCPs is a “Dark-sider” then, since I like all the power plants I would be an Airgun Enthusiast. …yeah, I resemble that remark 🙂


    • Hank, I think it is probably a range of manufacturing tolerances. I don’t know if the foster fitting has an official spec like cartridges do. I read an article about that somewhere. It may have been in Hard Air.

      Airgun Enthusiast is much more pleasant in polite company than “airgun addict” or “gun nut.”

  6. We human beans just love to make the uncomplicated complicated, no matter what it is; that is why the technology that adheres to the KISS principle the most is best – at least when it comes to FM World.

    • FM,

      My favorite KISS hunting weapon is a Holmegaard style bow. I’ve hunted small game and deer with them for decades.

      Using hand tools you can make one from commonly available hardwoods in a couple of hours. With power tools, I can turn a stave (piece of log) into a shooting bow in half an hour.

  7. FM
    Myself as a human being, not a human bean, I certainly try to keep things simple.
    Sorry my friend but I couldn’t resist, I have a strange sense of humor…

  8. Sure is frustrating when you need to buy yet another fitting to charge a new gun. Don’t even get me started on the Chinese pumps and compressors using 10mm fittings instead of 1/8 bsp!

  9. BB and ‘dark side’ readers,

    Slightly off topic. I need some advice so a little background first. I started with springers (very) long time ago. I like and often use them, but more recently I added – one by one – a few PCPs to my stable. You could say I straddle the light (?) and dark sides. The rest of the story is a classic. With my first PCP I bought a hand pump. Some time later a 300bar AV Carbon-Fiber bottle was added to make things easier. After some frustration with dive and paintball shops, I finally got a compressor to fill the bottle. Now I am done! Except, that I still have a lot to learn in the field of PCPs, and it is the reason for my question.

    I have guns rated to both 200 bar and 300 bar, which I would like to fill from the same bottle, but it has a fixed regulator adjusted to about 2,800 psi. Any recommendation for an adjustable bottle regulator to replace the current one? Short of getting a second bottle, any other suggestion?

    Thanks to all,


    • Henry_TX,

      The regulated tank works well for a tethered PCP and not so well as a Fill Station.
      take the regulator off of the valve if that is possible.

      Get a a regular on-off valve as a replacement if the above won’t work
      All my 200 and 300 BAR cylinders have a slow flow restrictor to meter the rate of fill to avoid burning and mechanical damage to seals (typically O-Rings) in the fill gear as well as the airgun.


    • Henry,

      If it’s possible I would remove that regulator from your air tank. You don’t need that. Just fill each airgun to the max and be done with it.


  10. B.B. and Readership,

    Thank you all again for your prayers and well wishes.
    They have worked thus far.
    The procedure was textbook according to the doctors and that is how it looked from the insiders perspective as well. Although i have an eyeshield on the view out looks very promising about 3+ hours after IOL implantation. I think the pour over Jacobs coffee, orange juice and Muesli Bread toast helps with the outlook too!
    Getting my eyedrops recording grid set up to comply with my hospital discharge orders.
    I hope to have more to say on PCP Cylinder/Fill station adaptor simplification.
    I will close for now with one Darks-Sider’s though; the shooting performance increase that PCPs bring to airguns are worth a little effort at ORGANIZATION beside of throwing it all in a drawer. Think shadows…Bob M knows what i’m talking about!

    Thank you all again you are a wonderful group of people!
    more later,


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