I am trying to pull the shaft out of the armrest on a 68 280. I have the armrest off with the shaft in it. I have it off and the old leather stripped off it. At the end of the shaft holding it on there is a bronze colored big disk (see photo). The arm rotates around this disk and shaft. The disk has 4 slots on its circular perimeter and a 7 mm what looks like a bolt head but it may not be a bolt but a cast part of the disk. I can't get it loose and it looks cast in place. Its odd, usually everything on these cars is so logical. Does anyone know if this is a bolt or is there a trick to getting this disk off so I can pull the shaft out.

Thank you