Nickel-titanium NiTi tools are much more flexible suitable for curved and narrow canal which , have better cutting capacity, they have a shape memory (always return to their original shape). 

Manual files NiTi type K (Kerr) best for finding canals and working the thin root canals. With a tightly twisted steel spiral, four cutting edges (low ability of cutting), flexible – provide safety. Low ability to transport outside the cut dentin. Files can be re-sterilized in a steam autoclave at 134 degrees C

length	long 31, Medium 25 mm, short 21 mm
size	15, 15-40, 45 – 80