Builders have been tacking accessories to concrete for hundreds of years. One of the oldest fasteners known to the industry is the pre-set anchor. If properly installed, the pre-set anchor fills its mission by providing indisputable holding power and once in place, by simplifying fastening. But the pre-set anchor has one serious drawback: they complicate the placement and curing of concrete. And the work crew must place them carefully in just the right spot, otherwise, they are useless. As an alternative, the builder may install his anchors after the concrete hardens. A popular way to do this is first to drill a hole in the hardened concrete, then to insert the anchor. One popular type is the expansion-shield bolt anchor. This device employs a lead or alloy sleeve (shield) in which a bolt is inserted. As the bolt is threaded into place, the sleeve expands. It grips the concrete, providing sufficient holding power to keep the accessory firmly attached. Another machine-bolt anchor is a hammer-set device. This type consists of a tubular expansion sleeve and a conical expander nut. The sleeve, along with the nut, is dropped into the hole, nut down the anchor slips about half way in and is driven flush with the hole with a hammer. Manufactures point to several advantages of the tubular, single-slit anchor. It has a rigid grip, even in holes that are unevenly drilled, and requires a smaller, shallower hole than many other machine-bolt types. It also has substantial holding power even in hollow material and interference with reinforcing bars is minimal. In recent years construction men have been turning more and more to still another way of installing anchors. They have been shooting pins and studs directly into the concrete by means of an explosive powder-actuated device. The tool itself is a pistol-like instrument that is easily loaded and easily handled. The workman inserts the explosive and the fastener into a forward chamber, then closes the handle and trigger assembly. He holds the tool against the concrete, depresses the barrel and pulls the trigger. The tool fires and the fastener is set instantly. As an alternative to the use of explosive charges, hand tools can also be used to set threaded studs, drive pins or wire loop fasteners into concrete without drilling or plugging.