N 6539 is a 4 in L bi-fold door snugger that snaps into the center of the bi-fold door track. The guide pin (N 6545) is inserted between the two springs in the nylon snugger housing. As the door is closed, the snugger slides in the track and makes contact with the opposite set of doors. This applies pressure evenly between guide pins. This causes them to remain in the closed position until one of the sets is grabbed by the knob and pulled outward. Used on Acme bi-fold doors.