Some of the XJ bump-stops do not unscrew, they are pressed into the metal retaining cup.
Others are crimped into the metal cup which then has a threaded bolt-like extension which screws the entire unit into the Jeep.
Not exactly sure of the years when the press/pop/push in units began.
My 97' XJ had this type
https://www.quadratec.com/products/76058_074X_PG.htm
These are SO MUCH FUN ( NOT ) to install new.
While both my Comanches ( 88' & 89') had/have the screw in type
https://www.quadratec.com/products/56021_100.htm
Good Luck!