The metal inserts are a plus if your bolts are long enough. What I did for a easy install was to press out the metal inserts & measured the dia of hex bolt heads. On mine I drilled out the holes where inserts where...with a "Q" size drill. That made a real tight push fit...and pressed the stack on. This avoids taking the bolts out & getting longer ones. Also you avoid creating air leaks. Simple. Capt,n