A pair of foot-size metal plates, one atop the other, secured together by a compressible material, the upper plate having a hinged heel portion which can be moved downwardly by heel pressure. The upper plate has straps for attachment to a foot or shoe, and the lower plate has front and rear axles which...http://www.google.fr/patents/US4061348?utm_source=gb-gplus-shareBrevet US4061348 - Roller skates
