A fastening tool assembly is provided with a housing with a contact surface, a longitudinal magazine receptacle, and a fastener outlet provided through the contact surface. A magazine body is received within the magazine receptacle to translate to a retracted position whereby a proximal end is adjacent the fastener outlet to store fasteners within the receptacle and to convey the fasteners to the fastener outlet, and to translate to an extended position whereby the body extends at least partially out of the receptacle for receipt of fasteners to the receptacle. A blocker is mounted to a side of the magazine body spaced apart from the fastener intake side. The blocker has a transverse width greater than a width of the body for blocking intake of fasteners to a wrong side of the body. Instructional indicia are provided on the blocker to instruct a user regarding proper fastener installation.