Kit includes two exhausts as shown above.

Here's a set of resin exhausts for the PV-1 Ventura Exhausts from Ultracast.   These exhausts are designed for the Revell kit. 

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Revell kit part compared to Ultracast replacement exhaust.

There are 2 exhausts in each set.  

These are very nicely master exhausts and are a big improvement over the Revell kit parts.