Many of us are used to padlocks with a locking hook and a rectangular body, or disc locks, which are padlocks with a disk-shaped body and a small curved bar rather than a hook. When you rent a self-storage unit, many facilities will recommend using disc locks as the bar is strong, shorter, and harder to split with bolt cutters.
Less well known are cylinder locks, which appear a bit strange at first glance. A cylinder lock is literally in the shape of a cylinder, with no locking bar. They work with the latch plates on roll-up doors. Not all self-storage units have this configuration, but for those that do, the cylinder lock is a great idea.
The cylindrical lock fits in an elongated hole on the left side of the latch plate. This opening should have a slightly arched top and a flat bottom, that corresponds to the arched top and flat bottom on the shaft of the cylinder lock. To lock your unit, with the key in the cylinder lock, put it in the opening flat end down and turn until the keyhole is in the three o'clock position, then remove the key.
In place, a cylinder lock resembles a regular door lock. They cost about as much as disc locks and are very secure. If you have a unit with a roll-up door, ask your self-storage facility if they support cylinder locks, and if possible buy one from the facility. They should carry the right type for their units.