I have a project in which I need to find a part that would work as follows: - Imagine a smooth steel rod that is for instance .5 inches in diameter. Now imagine a block with a hole in it that fits around this rod. This block needs to slide easily and smoothly on the rod. However, sometimes I want to secure this block to the rod so it does not slide. It needs to be electrically controlled. At this point I'm thinking magnetic so it is just attracted to the rod. However, if it causes something inside the block to move and clamp to the rod that is fine too. This way the rod could be stainless steel or something non-magnetic. The duty cycle does not need to be 100%. Someone PLEASE tell me some type of device exists and point me where to find such a thing.