On many of full size traction engine boilers and some models , in the us don't use a bushing for any penetration's where they can get like 3 threads. Some of the crown sheets don't have a bushing where the fusible plug penetrates. Alot of the models and or new boilers do have bushings welded into the plate penetrations partially for better wear life , partially because stronger and partially because it looks better and partially because some are required by pipe size.