These holding devices mount directly to the lathe headstock spindle. In the vertical mill the spindle axis is vertically oriented. Machines may have load sensing systems on spindle and axis drives, but some do not. The spinning wheel replaced the earlier method of hand spinning with a spindle. Clathrin aids in the congression of chromosomes by stabilizing kinetochore fibers of the mitotic spindle. The mitotic spindle then forms between the two centrosomes. These microtubules form direct connections with the kinetochores in the mitotic spindle. Kinetochores emit anaphase-inhibition signals until their attachment to the mitotic spindle. Most of the microtubules that form the mitotic spindle originate from the centrosome. However these astral microtubules do not interact with the mitotic spindle itself. Chromosomes are thus unable to achieve a metaphase spindle configuration. Calcium is a necessary ion in the formation of the mitotic spindle. Cells divide along the line connecting two centrosomes of the spindle apparatus. It is usually attached to a metal face plate attached to the spindle. Holding the fibre at a slight angle to the spindle produced the necessary twist.