On the aftermarket midpipes the flare is bigger than the stock. My off raod H kit came with a space that fits inside the driver side piping to make a better seal when bolted to the manafolds.My cousing did not nor did my best friends. Both of there's leaks, or sounds like a leak from the driver side. You can tighten it up all the way and you'll still hear it unless you get that spacer.