Harness stitching sheaths
Someone asked me recently- "OK, do you not like the lock stitch?"
My answer was: How big a deal this is depends on how hard you are on your leather. but- the double needle method has two COMPLETELY STITCHED threads going through each hole. So if you cut a thread, you don't lose the seam.
With lockstitch, if you cut a thread, it starts unlocking and you lose the whole seam, not half. With the double needle system, you don't even have to remove the broken thread to repair, you just overstitch 4 stitches each side of the broken thread.
Now, in survival terms, that means in one of our double seamed sheaths that you have something like 6 feet of thread available for an emergency, without touching the inner seam at all, and you could pull 3 feet of that out and still have a sheath.
The truth is, EVERY commercial leather sheath and about 80% of the maker made custom sheaths are lockstitched and they don't seem to have major issues most of the time. But if you get into quality harness for real range use, it's all going to be double needle stitched. and that's why.
I have several pieces of gear that are lockstitched and haven't had too many problems, but I have broken a few seams open at inconvenient times. Each time, that ends up with me, in the field, doing a harness stitch repair.
