Guide to cylinder connections

Confused about CO2 cylinder types and connections?

There are quite a few Different types of cylinder available for us to use in our aquariums and people are often confused as to which type of cylinder and what connections it may use.

These can be split into 2 main types

Standard refillable cylinders including CO2 Fire Extinguishers

These include various sizes (1kg, 2kg, 5kg etc) which are available from places like BOC, Energas, Pub gas suppliers, Hydroponics and Aquatic shops.

In most countries like Europe, Oceania and Asia the connection is called BS341 / DIN477 / W21.8x14, but also you may find other names depending on the country :

  • German Standard DIN 477 No.6
  • Swiss Standard SN 219505 No.7
  • British Standard BS 341 No.8
  • French Standard NF type C
  • Spanish Standard ITC EP-6, Tipo C
  • Netherland Standard NEN 3268, RU 1
  • Italy Standard UNI 4406
  • Australian / Oceania Standard Type 30
  • Japan JIS B 8246

In North America, connection standard is CGA320 and is used in most refillable CO2 tanks.

Smaller types disposable and refillable bottles

These can be split into 3 types.

  1. Sodastream (Contain around 500g of CO2) : 

    These have special threads only produced by sodastream these are all the same connection except if you get the cylinders from New Zealand or Australia which are different from the rest of the world.

    You need specially designed adapter to use it with standard CO2 regulator:

    The huge advantage of this type of bottles is that you can obtain them from most supermarkets around the world.

  2. Non-aquatic disposable types. 

    DIY disposable welding CO2. They contain 500g, 600g and 1kg of CO2. The connection Is an M10x1. These can be bought at places like Machine Mart, Halfords, eBay etc. You need specially designed adapter to use it with standard CO2 regulator:

  3. Aquatic disposable cartridge type.

This is the most expensive way of adding co2 to your aquarium. These come in various sizes ranging from 20-95g. This type of cartridges are not refillable and all the different makers use their own special connection for own type regulator. They can be bought from your local fish shop and eBay.

Those are few examples of different thread types used in disposable cartridges :

3/8-24UNF - 16g cylinder

5/8-24UNF - 74g cylinder

M16*1.5 - 95g cylinder

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