Abstract: Closer comprises a cylindrical housing defined by a front end and a rear end, the housing being formed with an axial bore having an enlargement in the front end. An air-driven cylinder is fixedly mounted in the bore and has an axial drive shaft reciprocable therein extending toward the front end and terminating in an impact head normally in an inward position. Reciprocably disposed in the enlargement is an annular trigger loosely surrounding the impact head and normally in an outward position extending down beyond the front end of the housing and movable to an inward position when the housing is lightly depressed over the fastener. An actuator in the housing is moved by the trigger as it approaches its inward position to activate the cylinder and slam the impact head downward to close the fastener. In a modification the cylinder is replaced by a solenoid.