Answer:
Spindle fibers are apart of a spindle apparatus that transports chromosomes during mitosis and meiosis to make sure their is a even chromosome distribution between the daughter cells.
Explanation:
Basically, they transport the chromosomes during mitosis and meiosis to ensure even chromosome distribution between daughter cells. They keep the chromosomes organized during the entire process to make sure there's no incomplete sets of chromosomes.
I'm not quite sure if you meant this or the Spindle (textiles), in that case I'll include information on that one as well. A spindle is a straight spike that twists fibers such as wool, flax, hemp, and cotton into yarn.