The knife geometry must match the material being cut. For heavy leather soles, a thicker blade with a double-bevel edge is necessary to prevent deflection. For synthetic uppers or linings, a thinner, teflon-coated blade helps reduce friction and prevents the material from melting or sticking to the knife during high-speed oscillation. Always verify the shank diameter and locking mechanism (e.g., flat-back or round-shank) to ensure compatibility with your specific cutting machinery like Atom, Comelz, or Teseo.