 K fibers/Kinetochore microtubules are the third important subclass of mitotic microtubules.These microtubules form direct connections with the kinetochores in the mitotic spindle.Each K fiber is composed of 20–40 parallel microtubules, forming a strong tube which is attached at one end to the centrosome and on the other to the kinetochore, located in the center of each chromosome.