A staple or nail gun assembly includes a staple or nail gun, a cap feeding device and a cap having a peripheral rim disposed on its underside, a marginal edge on its upper side adjacent a central portion having the shape of a truncated cone. The staple or nail gun and the cap feeding device are generally disposed at opposite ends of the handle of the staple or nail gun. The cap feeding device includes a base, a cap container and a shuttle, and feeds caps sequentially as they are affixed by the gun. The caps are coaxially stacked by means of a coaxial plastic cord or wire with retaining means at the respective ends or in a tubular container with a flanged end. The caps may also be stacked on a rod or held together by melting.