I don't know for sure but when I asked if the steel were replaceable the reply was yes and they are glued into the cap. To replace heat the cap up and the glue loosens its grip from the fire steel. The glue recommended to me to use for securing a replacement steel was gorilla glue.

I like this design over the Exotac method of threading the steel. It is simple and doesn't force me to purchase a steel with threads or cut my own threads.

Hmm just re-reading this and may have I misunderstood your question. Above I describe how the steel is secured to the caps. The caps have threads on them and they screw into the tube. The caps can screw onto the tube with the steel inside the tube (when carrying/storing) or outside the tube (when striking/scraping).