The AAR/APTA TypeH TightLock coupler is a Janney automatic coupler typically used on North American mainline passenger cars. TypeH couplers have mechanical features to reduce slack action and improve safety, but remains compatible with Janney/AAR TypeE and TypeF couplers. TypeH couplers may also be fitted with automatic air and electrical connections. Management and development of TypeH coupler standards have been transferred from the AAR to American Public Transportation Association (APTA). The AAR/APTA standard mounting height for TypeH couplers is 34.5 inches (876.3 mm) ATOR.