How to Choose Exhaust Gaskets for Your HArley

There two types, the stock conical-shaped ones, and the aftermarket flat gaskets. HD switched to the conical-shaped ones in the mid-90s. They do seal better in most situations, as long as your pipes are rounded or tapered at the port side.
Some aftermarket exhausts are cut flat on the port ends. If you use the conical gasket with the flat pipe, it will tend to push the gasket into the port, partially cutting off flow through the pipe.