A nose assembly for fitting onto a fastener installation tool for installing fasteners of the type in which a part of the fastener is broken off during the installation process, the nose being provided with a housing and a sleeve, the sleeve having a spring, and a collar which is movable within the housing against resistance of the spring, wherein plunger means are provided on the collar, and wherein the sleeve is threadably engaged with the collar, such that movement of the sleeve causes corresponding movement of the collar and plunger means, the plunger means being arranged to actuate a trigger thereby to open an air valve and allow a flow of compressed air through the tool, thereby to allow installation of the fastener into a workpiece.