The Knob Secure spacer provides a simple solution that will permanently stabilize the loose door knob condition. The Knob Secure spacer is the only solution that will stabilize the loose door knob and eliminate additional door damage while providing flexibility to change door knobs. The process takes less than 5 minutes per door and costs a fraction of the cost of a new door. Bi-fold doors are found in residential homes, apartments, condos, townhouses, commerical residential complexes, professional office buildings, high rise building and business office; literally any building may have a bi-fold door. PLR Solutions, LLC is committed to providing quality products and provides a money back guarantee, however note that we have never received a returned part.