elements are contemplated but should require no further explanation to those of ordinary skill in the art in the preferred embodiment of this invention a combined nail and washer are attached to the weight before the air cylinder is fired so that the dropping of the weight serves to drive the nail through the insulation 12 and into the roof deck 10 the nail and washer may be preassembled by manual or mechanical means and may be therefore accessible to an operator in a precombined state alternatively as shown in fig6 it is contemplated that the upper portion of the carriage may be provided with a mechanism for combining the nail and washer one or more reciprocating plungers are reciprocable in a respective cylinder 52 supported by the members 33 each carrying a magnet 63 at its lower end for engaging the head of a nail vertically aligned therebelow for supporting a circular washer 20 is a circular member 54 having a central cavity the plunger is reciprocated to drive the nail through the washer to combine the two the movement of each plunger is operator controlled by a suitable valving arrangement actuated by a respective handle 55 on the upper portion of the carriage the same valve also operates the insertion prongs 66 it is contemplated that the number of such mechanism.