Door hardware including hinges, locks, closers, and panic hardware must be properly installed for safe and functional doors. Hinge installation is critical for door operation. Most residential and light commercial doors use three hinges spaced vertically. The top hinge should be 10 inches from the top of the door, the bottom hinge 10 inches from the bottom, and a middle hinge centered between. Heavy doors may require four hinges. Hinge fasteners must be screws through the frame into solid wood or structural members. Fastening to drywall or hollow material fails. Commercial-grade hinges use heavy-duty screws. Lock installation begins with boring holes for the lock body and strike plate. Hole size must match the lock specification. Strike plates are mortised into the jamb to be flush with the surface. Latch bolts must engage the strike plate properly for security. Deadbolt locks provide security when engaged. Knob locks on entry doors must be supplemented with deadbolts. Fire-rated doors require specific hardware rated for fire applications. Closers control door closing speed and latching. Overhead closers mounted above the door operate a mechanical closing mechanism. Floor-mounted closers pull the door closed through a hydraulic mechanism at floor level. Closer adjustment balances closing speed with adequate force to latch the door. Panic hardware allows rapid egress from buildings during emergencies. Panic bars must release with minimum force per code. Exit devices controlling exit doors must be properly installed and maintained. Hardware finishes including paint, stain, or coating must be compatible with door material and provide durability. Stainless steel hardware resists corrosion in coastal areas.