EXTREMA RATIO- Golem S- Testudo ABS Fixed Blade Knife ( 4.5" Stainless Steel Bade) Extreme Ratio Knives have produced this magnificent knife, with the Tanto style blade made of N690 Stainless Cobalt Steel, which has extraordinary mechanical and cutting features. The sheaths for this series are available in Black INPAX (similar to Kydex) only. All sheaths are ambidextrous and have multiple anchoring points.