Swapping Pin Lock Corny Kegs to Ball Locks

Whether you’ve decided to keg your homebrew or ferment inside a keg, the first thing youll need to do is find a couple used kegs. By far the cheapest and easiest to find are the old soda kegs, or otherwise affectionately known as Corny kegs. They are usually found in 5 gallon sizes, but occasionally 2.5 gallon sizes are available.

What are Corny Kegs?

Cornelius – or “Corny” for short – kegs were used extensively by the soft drink industry to distribute their soda around the United States. Corny kegs have largely been phased out of the soda manufacturers in favor of much cheaper Bag-In-Box (BIB) packages full of concentrated syrup instead.

With this switch by the soda industry, many kegs that were in circulation were offered to homebrewers to help keg their beer instead. These kegs are perfect for homebrewing since they can handle pressure significantly above what beer ever needs, they are stainless steel which resist infections and are pretty cheap considering they are almost always found used.

Two Types of Corny Kegs

There are two main types of Corny kegs: “pin-lock” and “ball-lock” styles. While the base canister is similar between both styles, the difference is in the posts on top that connect the liquid and gas lines.

Pin lock kegs were primarily used by the Coca-Cola company, while ball lock kegs were used mostly by Pepsi.

While looking around for a refurbished Corny keg, it is important to know which style you are going to ultimately settle on, and which style you find in the wild. Luckily, you can change one style to the other, but there are a few “gotchas” that you need to watch out first.

How to Change a Pin Lock to a Ball Lock (or Vice-Versa)

The first step is to decide which style you want to settle on. I chose the ball-lock style because it was easier to find since most homebrewers choose ball locks, and also the fact that my Kegerator conversion kit already came with ball lock connections.

I found my two Corny kegs for about $35 a piece on Facebook Marketplace, but they happened to be pin lock kegs. Not an issue I thought – I’ll just replace the connection posts up top easily.

You will need to determine the size of your post threads before you buy the replacements. There are two different sized posts: one has a 19/32-18 thread and the other has a 9/16-18 thread.

Option 1: Look at the Top

One of the easiest ways to tell is to look at the top of the keg. If the rubber handles are a full circle the whole way around, they are Firestone/Spartanburg. If the rubber is notched and a “broken circle” near the post areas, then it is a Cornelius type.

In the picture at the top of this post, you can see mine are Firestone kegs since both of their black rubber tops form a full circle.

Option 2: Look at the Name

You can also look at the manufacturer that is stamped on the outside stainless steel shell of the keg.

• If the keg is a Firestone, Spartanburg or Hoover, then both post threads are likely 9/16-18.
• If the keg is a Cornelius (yes, same name as the general keg, but ignore this fact for now), then the post’s thread size is 19/32-18.

Option 3: Test the Thread Size

Another way to tell the thread size is by going to Home Depot or Lowes and buying two nuts, one of each size and seeing which one fits. Be forewarned though – the 19/32 will sometimes fit on the 9/16 thread, but not the other way around.

Buying Replacement Posts

Most replacement post sets will come with both the liquid and gas posts as well as the required spring and poppits that go inside.

You can identify the gas post by finding the one post that has cuts at the bottom of it. This marking is meant to identify “gas”, but I’m honestly not sure if it even matters which side each of the posts go on since they are virtually the same outside of the cut markings on the one. I think the markings are there just so you can identify which post is which after they have been connected to your keg and you are about to attach the lines.

Other Maintenance On Refurbished Kegs

It is probably a good idea to get a new o-ring set for your keg as well as a tube of silicone grease. Refurbished kegs are famous for having small leaks from time to time, and having new rings and fresh grease to add will usually fix the problem immediately. O-ring sets are usually universal and will work with any corny keg style.

Pro Tip: Vaseline will work in a pinch in replacement of the silicone grease.