An aircraft assembly including a first part having a pin and a second part having a hook that is movable in an engagement plane to engage the pin to hold the first part in a condition relative to the second part. The pin has a prominent central portion and one or more axially spaced outer portions, the prominent portion is prominent with respect to the outer portions in the engagement plane to cause contact to be made between the hook and the pin within the central portion of the pin, rather than the outer portions of the pin.