Hollow-handle razor knife with blade slide

In combination with a blade, a razor knife comprising:

• a hollow elongated housing having a front end slot;
• a slide seat part having a formation removably retaining the blade, the seat part being displaceable longitudinally in the housing through the slot between a longitudinally forwardly extended position with the blade retained on the formation lying mainly outside the housing and a longitudinally rearwardly retracted position with the blade retained on the formation wholly inside the housing;
• and
• a retaining part slidable on the seat part in a direction between a closed position overlying the blade and holding it in place on the seat part and an open position exposing the blade on the formation and allowing it to be removed therefrom, the parts having stop faces engageable in a locked position with each other to prevent sliding of the retaining part on the seat part in the direction, whereby the retaining part is displaceable together with the slide seat part to the extended and retracted positions, one of the stop faces being displaceable transversely to the other into an actuated position to allow the parts to slide relative to each other in the direction, whereby in the extended position of the seat part and the open position of the retaining part the blade is exposed outside the housing and in not retained in place on the seat part by the retaining part.