The keyed lock cylinder on most metal file cabinets is a standard, single-post locking mechanism. The lock usually has a thumb tab that engages under the lip of the file cabinet, and some have a notch that engages a lock bar on the side of the cabinet to lock the lower drawers. Replacing a lock for a metal file cabinet due to damage or loss of a key is a straightforward process. Replacement locks are available at home improvement centres.
Open the top drawer of the metal file cabinet. This is the drawer that has the lock. Look on the inside corner of the drawer where the lock secures. There is either a C-clip securing the lock shank or a nut threaded onto the shank.
Pry the C-clip away from the lock with a flathead screwdriver, if your current lock uses a C-clip. Turn the nut counter-clockwise with a wrench, if your lock uses a nut to secure it to the drawer. Pull the lock body out of the drawer through the front.
Insert the key into the new file cabinet lock. Push the lock into the front of the drawer with the key teeth pointing down.
Slide the C-clip over the lock shank inside the drawer. The C-clip should fit into a groove on the shank that is flush with the inside of the drawer front. It might be necessary to use a screwdriver to push the C-clip in place fully.
Thread the nut onto the lock shank, if you are installing a lock that uses a nut instead of a C-clip. Tighten the nut with a wrench.
Operate the lock with the key. If your metal file cabinet has a rod on the inside, ensure the lock tab engages the rod when you lock the drawer. Loosen the lock and adjust as necessary.