A loose leaf binder having a pair of separable front and back cover members respectively hinged to relatively rigid interconnecting numbers of L-shaped cross-section adatped to be interfitted in overlapped relation to provide an expansible back for the binder. The L-shaped back-forming members are respectively...http://www.google.es/patents/US4060330?utm_source=gb-gplus-sharePatente US4060330 - Loose leaf binder locking device
