The crowned tooth gear coupling is a key component in modern heavy-duty shaft transmission; its crowned tooth meshing compensates angular, radial and axial misalignment between shafts. In China, the GICL, NGCL and GCLD series under GB/T standards are mainstream and widely used in metallurgy, mining and power industries. American gear couplings are based on AGMA standards; brands such as Falk, Lovejoy and Kop-Flex have deep influence in mining, energy and marine fields. AGMA products emphasize clear grading of rated torque and allowable speed, with structures biased toward durability and serviceability. Compared with domestic GICL, AGMA gear couplings offer richer choices in extra-high torque and special bore specifications. Standard systems differ markedly: domestic products follow GB/T crowned tooth coupling standards, Japan uses JIS, the US uses AGMA, and Europe uses DIN/ISO. During selection, note the differences in torque and speed units (N·m vs lb·in) and allowable misalignment definitions; do not apply parameters directly across systems. Whether domestic or imported, correct installation, alignment and lubrication are prerequisites for coupling life. Mastering standard differences and structural features lets the crowned tooth coupling perform reliably in the transmission system.