I recently ordered a pair of used ball lock Cornelius kegs from a website. One of the posts of one of the kegs is slightly bigger than the other. In order to get the beer out line onto the keg in the first place, I needed a mallet. I could not get the out line off even with a monkey wrench and a screwdriver. I eventually chopped the ball lock connector in half with a dremel tool.

The problem post is 15.81 mm. I was able to measure 4 other posts, on my various other kegs. They measure 15.53mm, 15.63mm, 15.47mm, 15.83mm. This is about 0.3mm of difference between the biggest and smallest parts. I have never put a connector on the 15.83mm post.

For my day job, I am an engineer. When two parts are supposed to snap together, it is important to machine those parts to a precise size, or you will find yourself jamming things together and prying them apart. 0.3 mm sounds very small, but it makes a huge difference in whether two parts can fit.

On my old keg, I have always had trouble with one of the posts. I always have to fight to get connectors on and off of it. I suspect that I have an issue with an incorrectly sized post or an incorrectly sized connector.

How big is a ball lock post supposed to be? Are sticky, difficult connectors a common problem?

1 Answer 1


Some of the difference you are seeing is likely the difference between the gas and liquid lines. These are not designed to be interchangeable, but they are close enough that it's tough to see without close examination. It is possible that when they assembled the kegs to ship to you they mixed up the posts. Commonly the gas post will have little horizontal cuts around it's base. Check to see if your gas fittings have them, and your liquid do not.

Also, a bit of keg lube can help with taking the posts on and off if they are difficult to use. It's a simple food safe lubricant that will help extend the life of the rubber seals.

Other than that, I am also surprised at the variance. Even allowing that they should fall into two different categories that still leaves you with a higher difference I would have expected. I suppose that could be because the seal is really formed by the o-rings and that allows for a larger tolerance.

  • 2
    Are the gas and beer sides not interchangable? Making them that similar was a terrible design choice. Apr 12, 2017 at 14:49
  • No, they are not interchangeable. You use a grey connector for gas and a black one for beer.
    – Denny Conn
    Apr 12, 2017 at 15:46
  • 1
    The gas connector usually goes on and off both post types relatively easily. The beverage connector however does not want to easily go on and off on a gas post. At least in my experience.
    – brewchez
    Apr 12, 2017 at 16:23

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