The invention relates to a single-firing trigger mechanism for a nailing machine with a receptacle for receiving a swiveling element pivotably on a second positioning shaft. The other end of the swiveling element with a torsion spring is pivotally connected to a contact element on a third positioning shaft and, in addition, the top end of the contact element is disposed at a height to be in contact with a safety lever. The safety lever should be extended into the inside of the trigger and pressed against the contact element so as to be shifted in the direction of the firing pin. Thereafter, the user can press down the trigger again, thereby causing the contact element to be in contact of the firing pin for the next single-firing operation.

A trigger device for staplers includes a trigger pivotably connected to a stapler body and an opening is defined through the trigger. A cam device is rotatably engaged with the trigger and a lower end of an activating member is connected to the cam device so that the activating member is moved up and down by rotating the cam device. A safety plate is slidably connected to the stapler body and a distal end of the safety plate is located in correspondence with the opening of the trigger.

A single-shot nail stapler includes a valve and a valve-opening rod for pushing the valve open. A major trigger includes two side members each with an upper portion pivotally attached to a portion of the single-shot nail stapler and a lower portion defining a substantially horizontal slit and a substantially vertical slot with an upper end and a lower end. A slide includes two side members each including a fin formed thereon and defining an inclined slot with an upper left end and a lower right end. The fins are movable in the substantially horizontal slits of the major trigger. A secondary trigger includes an upper portion, a lower portion and an aperture defined in the lower portion of the secondary trigger. A pin is fit in the aperture of the secondary trigger and movable in the inclined slots of the slide and the substantially vertical slots of the major trigger. Two springs are each compressed between the major trigger and each of the slide members of the slide. A security element extends movably between the side members of the major trigger for pushing the upper portion of the secondary trigger.

A nailer includes a gun body, a safety lever, a push device, and a contact trigger device. The push device includes an urging member, and a torsion spring, and the contact trigger device includes a mounting member, an O-ring, an elongated contact member, and an elastic member. The torsion spring has an elastic force smaller than that of the elastic member. Thus, the nailer is operated only when the first end of the safety lever is initially pressed on a workpiece and the trigger is then pressed, thereby providing a safety function to the user.

A nail gun has a free end 19a and central potion of a trigger arm 19 positioned within a trigger 11, on an upper end 12a of a safety portion 12 and at a plunger 17, respectively. When the trigger 11 is pivoted on its pivot end 16, pivoting movement of the trigger 11 moves a pivot end 18 of the trigger arm 19 to press the central portion of the trigger arm 19 into contact with the plunger 17 and, with the plunger 17 serving as a fulcrum, to press the free end 19a downward against the upper end 12a of the safety portion 12. If downward movement of the safety portion 12 is obstructed when the trigger 11 is pivoted, the upper end 12a contacted by the free end 19a of the trigger arm 19 serves as a fulcrum around which the trigger arm 19 pivots with movement of the trigger 11, whereupon the central portion of the trigger arm 19 presses the plunger 17 inward so that an activation switch 10 activates a blade 7 to eject a nail through a nose piece 5.