* Bow size and hair density: Bow size can vary, and so can the density of the hair. A larger bow might hold more hairs, while a more tightly packed bow might use fewer.
* Bow maker preference: Bow makers often have their own preferences for hair density.
* Individual needs: The player's personal preferences and the style of music they play can also affect the desired hair density.
However, a typical viola bow will hold somewhere between 100 and 200 hairs. This is just a general guideline, and the actual number can vary significantly.