Think of a magnetic field as basically a donut shape with force lines flowing in a circular pattern. Pretty strong, within reason. Now take one side of the donut away. Greatly weakened with little or no path for the force lines. The keeper is to protect that "donut" from being weakened. Some magnetic materials and shapes are more affected than others. Charles > What is the mechanism that keeper provides? On the face of it, why should > an increase in reluctance lead to the domains re-arranging? It's one of > those things that I know happens, but don't understand why! > > Peter Chadwick (out of the country again - no wonder I can never get in > the workshop!) MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.