How do you lock the rotation of a bone in an IK chain? How can you make an IK chain of bones where one of the bones does not rotate relative to it's parent bone but is still part of the IK chain?

Specific example: I have this simple arm rig with IK that I want to split the forearm so the wrist can rotate properly...

I tried putting the IK constraint on the 2nd forearm bone and making the IK chain 3, but the two forearm bones bend. How do I make them not bend while still having the arm move normally?


How do you keep those locked? Again, this is a pretty simple IK setup otherwise, until I wanted to split the wrist/forearm. Thanks for any help!
You need to use the IK Limit rotation found as shown below: