A winder is a control bone that bends multiple parallel bones by the same amount. It is used in the MHX rig for fingers (a single finger bone bends all three finger links) and for the spine (the back bone bends three or four spine bones). It can also be useful in other contexts, e.g. for male genitals or for ponytails, as was discussed in a previous blog post.
Winders are also useful for rigged hair, but here we often need to create several winders, one for each chain of links. Previously that was rather cumbersome, because the Add Winder tool had to be run for each chain, with the root of the chain active. With the latest update, several bones can be selected at once, and the tool automatically figures out which bones are the chain roots.
Select the bones that we want to make winders for. This is usually quite easy, because the Merge Rigs tool puts non-standard bones on a separate layer. Press the Add Winders button.The option box lets us select the bone layer where the winders live.We can now quickly pose the hair with the winders.
The winder pose results in a quite complex pose for the original deform bones, which would be tedious to create by hand. However, the individual bones can still be posed on top of the winder pose, if we want to refine the pose.