A tapered split nut with depressed by coil spring downward in a central hole of a outer cylinder body is installed so as it can move upward. A hanging bolt is inserted from the bottom while it is pushing said split nut up. Owing to the upward movement of the hanging bolt, the split nut moves downward...http://www.google.es/patents/US5468105?utm_source=gb-gplus-sharePatente US5468105 - Ceiling insert
