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One day I stumbled across CustomKydex and queried Kiah, the proprietor, about making just that one small piece for me. (Most of Kiah's plastic is more fantastic, much more elaborate and very cool.) The answer was yes, I replied with my specs, and my RAT and I sat by the mailbox.
While we were waiting, I used triangular files of two different sizes to remove the coating from the jigged section of my RC-4's spine. The firesteel requires a square-cornered striker and bare metal works better, so some of the black stuff had to go unless I wanted to strike with the knife's sharpened edge (which I don't). Thus modified, it works perfectly.
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As a package, it looks like it came that way from the factory -- it's simple, inexpensive and elegant. I'm liking it a lot.
(In case you're wondering, yes, it's raining out by my woodpile today.)
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Sharps: RAT Cutlery RC-4P MB
Sharps: Heartland leather
Links
CustomKydex
RAT Cutlery Co.
BladeForums thread