FITTING A REPLACEMENT KEY Fitting a replacement key to a lock is a relatively simple process: Look at your lock to determine whether or not it has a pin showing in the keyhole. If so, measure the pin diameter and check our items for a corresponding pin hole diameter size. If not, select one of our solid shank keys with a bit size closest to the size of your keyhole. The bit portion of our skeleton key blanks are left slightly oversized and may need to be filed down slightly to fit your keyhole and work the lock.