Bicycle Mechanics - How to remove bar plugs?

I want to get the rubber bar plugs off an old set of handlebars. Each plug has a flat-head screw that I can turn all day long but it doesn't seem to be allowing me to yank the plugs out. I'm assuming there's a wedge in there, like the wedge on a stem? How do I get them off?

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Back off the screw, but don't dis-engage it. Then tap it in to push the wedge out. The plug will loosen, but if it's been there a while might be stuck to the wall of the bar and need a firm tug to come out.

Velox End plugs, It may have rusted the nut onto the bolt, and you are just spinning the combination.

there is no wedge , just a couple flat washers and a star washer under the nut, slight grip to tighten the nut and so compress and expand the piece of rubber.

see if you can get some soapy water between bar plug and the metal tube that is the bar.

so you can pull it out with twisting and brute force-of-will ..

Thanks, fietsbob, that did the trick. No space to squirt soapy water due to the remnants of old bar tape between the plugs and the steel, but I managed to force in a flat-head screwdriver, giving me leverage to pry the plug far enough out that I could yank it. Sure enough, the washers and nut were rusted solid to the bolt and the plug came out with a shower of rust, disintegrating rubber, and flakes of bar tape.