I made this knife sheath today for my modified British MOD survival knife. The knife is 5mm thick high carbon steel which I brought down to a clip point. I also removed most of the finish but left it a little rough around the edges for a rustic look. This is my other post on this knife detailing the modifications I carried out; http://thesecretcamper.blogspot.co.uk/2012/07/customised-british-mod-survival-knife.html
The sheath is made of multiple layers of 4mm thick full grain leather,
stitched with nylon thread and given a waterproof dressing. It is a design based on Leodis Leather's Rat Cutlery sheath. Check out his vids on Youtube, they are very good if you are taking up leathercraft.
Its my first leathercraft project and I am happy with the results. I found it very relaxing, so this will be the first of many. My next project will be to make a sheath for my Ontario Cutlass machete (12") as it didn't come with one.