Abstract: A carpet knife having a housing, an active blade installed in the housing, and a blade clamping means having a clamping cover and a thumb screw. The housing has a thumb screw hole, a pin hole, at least one side guiding groove, and an active blade installation bar. The clamping cover has at least one side guiding bar having a wedge outer surface, and a rear eccentric guiding groove. The thumb screw has a head having an under surface and a shank formed on the under surface. The head has a pin formed on the under surface thereof which is able to enter and move in the rear eccentric guiding groove.

Abstract: A retractable utility knife has a housing, a blade seat forward slidably received in the housing, a blade fixed to the blade seat, a driving unit having an actuator protruding out from the housing and an actuator seat reciprocally slidable along the housing, a blade seat return spring linking the blade seat and the housing, and a blade change means. The blade of the retractable utility knife is also able to be locked when fully extended to avoid painstaking thumb pushing when works for mass workloads.

Abstract: A utility knife with step extending blade has a housing, a blade seat slidably received in the housing, a blade fixed to the blade seat, an actuator fixed to the blade seat and reciprocally slidable along the housing, a blade seat return spring linking the blade seat and the housing, a step extending control unit, and a blade change means. An extending length of the blade of the utility knife is step regulatable according to different thickness of workpiece, thus decreasing the possibility of break of the blade.

Abstract: A carpenter knife with locking member having a handle having a left shell and a right shell coupled together, a slit defined in the left shell, a stage formed rounding the slit; a knob being roughly of oval shape and having a central opening; a blade having a cutting edge and contained in and slidable with respect to the handle, an installing notch defined in the blade on a side opposite to the cutting edge; a blade seat contained in the handle, the blade seat having a bottom plate, two side walls, a spring tongue, and at least one installing protrusion, a top protrusion and a side protrusion formed on a free end of the spring tongue; and, a pin passing through the central opening of the knob and having a hole in which the top protrusion being firmly inserted in.

Abstract: A utility knife with an auto-retractable blade, having a housing containing a blade therein. An actuator is provide being fixed to a slider contained in the housing and slidable with respect to the housing. The slider, having an upper hook and a lower hook and being able to coact with an upper protrusion and a lower protrusion of a blade seat also contained in the housing, are able to automatically retract into the housing after the blade leaves a workpiece and before a user of the knife releases the actuator for extending the blade. The blade will not undesirably move backward in cutting.

Abstract: A carpenter knife with locking means having a handle having a left shell and a right shell coupled together, a slit defined in the left shell, a stage formed rounding the slit; a knob being roughly of oval shape and having a central opening; a blade having a cutting edge and contained in and slidable with respect to the handle, an installing notch defined in the blade on a side opposite to the cutting edge; a blade seat contained in the handle, the blade seat having bottom plate, two side walls, a spring tongue, and at least one installing protrusion, a top protrusion and a side protrusion formed on a free end of the spring tongue; and, a pin passing through the central opening of the knob and having a hole in which the top protrusion being firmly inserted in.