Just to let you know, I purchased the smallest version of the Firesteel and put it on my key ring (slightly smaller than my auto key). I added some plastic tubing (sourced from an aquarium shop) to fit over. I left a tiny bit at the end to make it easier to pull off when I want to use it.

I dispensed with the lanyard string and striker. My Spyderco Salt-1 knife works quite well to create sparks. Since the blade is H-1 steel, I tried the steel from the locking back. It works perfectly.

The following is a close up picture of my EDC keyring including Photon light and S4 Squirt minitool.