They should screw out easily. Sounds like someone used Loctite© to keep them in. That's what I did to mine after having to retrieve one of the threaded inserts from the club I had taped in the previous night. Try using some internal snap-ring pliers. Your mechanic or a machine shop will have them or try a Loew's/Home Depot or Sears tool section. If you don't plan on using thread locker once you get them out, just take the clips into one of the above stores and use a pair off the shelf. If anyone asks what your doing, just tell them you're making sure the tool will work for your intended purpose. Once the inserts removed, you don't need to purchase the pliers.
Not sure what size the threads are in the clip itself but the insert's internal thread should be 5/8x27 which fits most mic stands. Why do you want the insert removed?