Very ingenious expanding brass key fit into lock upside down. Shaft is hollow and has piston inside. When key was inserted into lock the piston was driven out along with the teeth that attached to it. It would be a difficult lock to pick since any key that would fit through keyhole would not have long enough teeth to drive tumblers. This key actually expands when it is inserted into lock. Two notches at bottom of teeth.
L. 7.5 x W. 4 x H. 4 cm (L. 2.95 x W. 1.6 x H. 1.6 in)