Abstract: A fastener installation tool is provided that is used to install a threaded nut onto a threaded fastener of the type having a non-circular recess in an end of the fastener that matingly engages with a male member that has a complementary shaped non-circular tip end to the non-circular recess. The fastener installation tool generally has a head, a gear, a socket, a key, a key holder and a spring. The key has a shank with a non-circular external surface that matingly engages with a non-circular aperture in the key holder. The mating engagement between the key and the key holder provides the key with resistance to rotation and permits the use of a lower gauge spring that facilitates replacement of the key from the fastener installation tool. The key, key holder and spring are also available as a kit for retrofitting a fastener installation tool.