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 mail 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. The base has a cap feeding chamber and-a cap holding chamber and a channel connecting the two chambers. The container is used to store staple or nail caps and to feed the caps to the cap feeding chamber of the base, one cap at a time. The shuttle is operatively associated with the channel of the base to move a cap at the cap feeding chamber towards the cap holding chamber through the channel by a distance equal to the diameter of the cap. 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.