When you look at any knife , the back spine is at 90 degrees from the sides of the blade. Right? Well, about two years ago, I bought a cheap folding knife ( about $ 6 ) and it was OK for me, but I noticed the spine of the knife was tilted to about 70 degrees. It didn't matter at all, and I thought ( what would you expect from a $6 knife ? Can't be perfect)

A few weeks ago, I was watching a few U-tubes and noticed a guy reviewing a knife and he mentioned specifically that this tilt in the spine was for scraping the ferro rod. Then I remembered an episode of Duall Survival when Copdy failed to start a fire and he asked Dave for his knife because the back of Cody's mora was rounded and Dave knife maybe squred ( for better friction with the ferro rod)

I went back to my "imperfect" knife and tested it with a ferro rod, and really it threw so much sparks I was afraid it would start fire ( I was sitting in my home office and expected the usual amount of sparks I get from other knives). The back of this knife works something like a Micro-chisel and really scrapes the ferro rod agressively. So, the rod may not last for long but you get better sparks.

A few days ago, I bought another cheap folder with two blades( I always wanted a folder with two blades) and noticed the same "imperfection" in thier backs.

Have you guys noticed this feature in your knives or is it not so wide-spread thing ?