Mossberg 500 shotguns utilize a dowel (or even chopsticks) cut to a certain length to limit magazine capacity.

Some aftermarket polymer followers have a recess in the tail that can accept the wooden dowel via press fit and become very stuck.

If that happens, the plug can be removed by pushing the follower in with a cleaning rod till the plug sticks out of the barrel female threads on the mag tube. Grab with a set of vise grips and wiggle free. Much simpler than removing the tube.