The Freak inserts are the most crucial part of the Freak barrel kit. Although paintballs are technically considered 68 caliber, they come in a variety of sizes. The Freak inserts come in 8 different sizes ranging from the small .679 to the large .695. It is very important for you to choose the right Freak insert for the particular paintballs you are shooting. The better fit your paintball has in the insert, the better accuracy and less broken paint you will have in your day. The most common size inserts used in the paintball world would be the .689 or .691. These two inserts cover the majority of paintballs on the market and should work well with all brands of paintballs.