This is an ingenious firekit design! The caps on each end (one with ferro rod the other with compass) are threaded on each side of the caps. This would allow you to thread the compass and rod either on the inside or outside of the barrel housing. Other barrel housings can be threaded onto an existing barrel housing to extend the assembly for more inside space. The rod and compass caps have thread protectors on the outside threads that need to be removed before turning them around on the barrel housing.