Ron Hood (www.survival.com) sells a 2" ferrocium rod that is much thinner (diameter) than the ones pictured above, like a really thick pencil lead. It seems it isn't just the surface area of the rod, but also its composition that matters because this very small rod throws off as many if not more sparks than its bigger brothers (I have the military Mg block and the rod with the lanyard & steel scraper too and I have compared them).
When I first used one, I thought it was going to break (too thin) from the pressure of the scraper on the flint. I've used my original rod about 2 dozen times now to start a tinder and it has never broken no matter how hard I've scraped it. I haven't tried to just break it with my fingers, but I've ordered a few more and when I get them I'll post a more formal review.
These firesticks have the advantage of being exceptionally small and so fitting into very small nooks in your survival kit. They are $4 if purchased in quantities of 2 or more, and they go down to $3 at a dozen, not a bad price for buying a bunch and spreading them around - make great christmas gifts. I'm not associated with Ron by the way, just a satisfied customer. If any one knows of a still less expensive place to buy these, let me know.