The Burton 3D pattern uses three inserts per side in a triangular layout, and it was the standard on Burton boards before they switched to the Channel system around 2014. If you're riding an older Burton, this is likely what you have.
The good news is that most modern bindings still include a 3D-compatible disc in the box, so you should have plenty of options. Brands like Union, Rome, and Ride typically offer multi-pattern discs that work with 4x4, 2x4, and 3D inserts all in one.
Just double-check the product details before buying to confirm 3D compatibility is included. If a binding doesn't come with a 3D disc, you can usually purchase one separately. Also keep in mind that 3D offers less fine-tuning for your stance width compared to newer systems, so you may have fewer micro-adjustment options when setting up your stance.