An apparatus, comprising: a shackle comprising: a body portion; a first leg extending from the body portion and including a first foot (116, 916); and a second leg extending from the body portion and including a second foot (116, 916) arranged parallel to the first foot (116, 916); wherein each foot (116, 916) comprises: a distal tip portion (150, 950) having a non-circular outer cross-section including a pair of parallel engagement surfaces connected by a pair of arcuate surfaces; a cylindrical portion having a circular outer cross-section; and a groove (118, 918) defined in the cylindrical portion; and a cross bar comprising: a housing including: an internal cavity; a pair of foot-receiving openings sized and configured to receive the cylindrical portions of the first and second feet (116, 916); a pair of tip-receiving openings aligned with the pair of foot-receiving openings and sized and configured to receive the distal tip portions (150, 950) of the first and second feet (116, 916); and a lock mechanism including a pair of deadbolts positioned in the housing, the lock mechanism having a locked state in which each deadbolt is engaged with the groove (118, 918) of a corresponding one of the feet (116, 916) and retains the corresponding foot (116, 916) within the housing, and an unlocked state in which the deadbolts do not prevent removal of the feet (116, 916) from the housing. a shackle comprising: a body portion; a first leg extending from the body portion and including a first foot (116, 916); and a second leg extending from the body portion and including a second foot (116, 916) arranged parallel to the first foot (116, 916); wherein each foot (116, 916) comprises: a distal tip portion (150, 950) having a non-circular outer cross-section including a pair of parallel engagement surfaces connected by a pair of arcuate surfaces; a cylindrical portion having a circular outer cross-section; and a groove (118, 918) defined in the cylindrical portion; and a body portion; a first leg extending from the body portion and including a first foot (116, 916); and a second leg extending from the body portion and including a second foot (116, 916) arranged parallel to the first foot (116, 916); wherein each foot (116, 916) comprises: a distal tip portion (150, 950) having a non-circular outer cross-section including a pair of parallel engagement surfaces connected by a pair of arcuate surfaces; a cylindrical portion having a circular outer cross-section; and a groove (118, 918) defined in the cylindrical portion; and a distal tip portion (150, 950) having a non-circular outer cross-section including a pair of parallel engagement surfaces connected by a pair of arcuate surfaces; a cylindrical portion having a circular outer cross-section; and a groove (118, 918) defined in the cylindrical portion; and a cross bar comprising: a housing including: an internal cavity; a pair of foot-receiving openings sized and configured to receive the cylindrical portions of the first and second feet (116, 916); a pair of tip-receiving openings aligned with the pair of foot-receiving openings and sized and configured to receive the distal tip portions (150, 950) of the first and second feet (116, 916); and a lock mechanism including a pair of deadbolts positioned in the housing, the lock mechanism having a locked state in which each deadbolt is engaged with the groove (118, 918) of a corresponding one of the feet (116, 916) and retains the corresponding foot (116, 916) within the housing, and an unlocked state in which the deadbolts do not prevent removal of the feet (116, 916) from the housing. a housing including: an internal cavity; a pair of foot-receiving openings sized and configured to receive the cylindrical portions of the first and second feet (116, 916); a pair of tip-receiving openings aligned with the pair of foot-receiving openings and sized and configured to receive the distal tip portions (150, 950) of the first and second feet (116, 916); and an internal cavity; a pair of foot-receiving openings sized and configured to receive the cylindrical portions of the first and second feet (116, 916); a pair of tip-receiving openings aligned with the pair of foot-receiving openings and sized and configured to receive the distal tip portions (150, 950) of the first and second feet (116, 916); and a lock mechanism including a pair of deadbolts positioned in the housing, the lock mechanism having a locked state in which each deadbolt is engaged with the groove (118, 918) of a corresponding one of the feet (116, 916) and retains the corresponding foot (116, 916) within the housing, and an unlocked state in which the deadbolts do not prevent removal of the feet (116, 916) from the housing.