I know very little about those myself, all I know they are hard to remove, they are designed to expand and clamp in the bar when tightened but ideally when the long screw is removed they should pop out, try soaking them with WD40 and then get a long neck pliers and see if they give, alternatively tap the opposite end with a wood mallet and they should really come out. If not its going to be a run to your local friendly mechanic, I am afraid.