A tool for driving a fastener pin into a substrate to secure a fastener body to the substrate for fixing insulation or other cladding, the tool being of the type comprising a fastener guide and a driving piston driven along the fastener guide by gas pressure to engage and drive the pin, the fastener guide being displaceable axially inwardly relative to the body of the tool in order to cock the tool for firing of the driving piston, wherein the tool comprises means for enabling the tool to push the fastener body through insulation or other cladding into engagement with the underlying substrate without putting the tool into a condition in which firing can occur, the tool being thereafter able to be put into a condition to permit firing to take place.