Review on 🏍️ Enhance Your Kawasaki Ninja 400 with Unlimited Rider Motorcycle Exhaust Middle Pipe - Stainless Steel Mid-Pipe 51mm Adapter Inlet Slip-On Connector (2018 Ninja400) by Kevin Vanlaere

Fits well but fits. The OE muffler connection has a gasket between the manifold and the muffler. This is part of the inside diameter of the muffler connection (see drawing of the factory muffler). So if you buy a midpipe made for the EX6F you may need a gasket to cover the 2-4mm gap in the spline. You don't need a seal with this center tube. Maybe just a high temperature sealant and that's it. Or none of the sealants helped me. First, this bike does not have an oxygen-sensing EFI. Some of these models (EU) do. Depending on what type of gasket you're using, this middle tube will work as well. This is what I used: https://www.amazon.com/gp/product/B088GV1KFK/ref=ppx_yo_dt_b_asin_title_o05_s01?ie=UTF8&psc=1 It's near the rear tire but I think it will be ok. You'll have to figure out how to hang it, as the included strap doesn't reach the factory muffler mount.