Trip Roller Assembly
This roller fits the pre-1999 BP555S style machines (pictured below). This is the roller actuates the opposite side of the switch that you press to dispense specific tape lengths.
If this roller gets squishy, it's time to replace. Make sure the indented ring is on the inner side when mounted on the machine. If the previous roller was installed correctly, reference which way the roller goes on when removing the old one.