This 4 into 1 merge collector with 2.5" outlet is used on our K-Swap header, and offered as an option to convert our 4-2-1 header into 4-1 header.
If your current header is a 4-2-1, this may convert your header into a 4-1 setup.
This may not fit other brands. Please contact us for fitment inquiry prior to ordering if you're unsure.