Abstract: A plastic hollow body contains a resilient spring plate. The spring plate is attached to the body at one end and, at another end, has an iron core. A hole in the body is slightly offset from a hole in the spring plate such that a pin extending through the hole in the body cannot pass through the hole in the spring plate until the spring plate is bent by a force from the spring. The pin then extends through the hole in the spring plate and the spring plate is locked onto a reduced diameter portion of the pin. The release of the pin is possible only by applying a magnet adjacent the iron core so as to move the spring plate from the locked position.