Originally Posted by Duck Dodgers 
Do you guys swap the m42-to-K adapter back and forth among lenses, or do you have one for each lens?
the M42 > K adapter locks into the camera's mount, it stays put on the camera, and you screw in and out the various M42 lenses.
If changing to K mount lenses the adapter has to be removed from the camera first.
Some people buy one adapter for each M42 lens and keep the adapter attached to the lens, making it into a K mount lens. One must remove the lock of the adapter so it does not lock into the camera and so that the lens can be removed with the adapter staying on it. That also saves having to put and remove the adapter on the camera when switching between K mount and M42 mount lenses.