Yes, the rubber piece/grommet that twists into the valve cover.
It's the modern version of a PCV valve.
It has a little rubber check valve built into it, under where the hose connects.
Go to your local Jeep dealer parts dept., and mention '4 litre blow-by', and they will (or at least should) know exactly what you are talking about.
DD: 98 ZJ Laredo 5.2, all stock
Wheeler/Beater: 93 ZJ Laredo
4.0, AW4, 231 conversion from 249
3" coil lift, JKS Adjustable Track Bar, JKS Quicker Discos, KOR lwr rad supt, Brush guard
Colorado Jeep Club Member 242 (4.0L)