A surface-mountable locking device includes a body within which is disposed: (1) a box configured to receive a pin and (2) a locking mechanism having a bolt configured to engage the pin when the pin is inserted into the box. Because the locking-mechanism bolt engages the pin within the box disposed in the body, the body protects the locking-mechanism bolt from tampering, creating a more secure lock than when the bolt is exposed. An adapter for attaching a chain link (or similar link) to the locking device is also disclosed. The adapter is configured on one end as a pin to engage the box and on the other end to engage a link.