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. In materials and heat treatment, domestic products mainly use 42CrMo and 45 steel, carburized and quenched to a tooth-surface hardness of HRC58-62. High-end foreign products often use alloy carburizing steel with vacuum heat treatment, giving better hardness uniformity and delaying pitting and wear. In summary, domestic crowned tooth couplings already have the technical basis to replace imports; users can select reasonably based on duty, budget and lead time. We will keep sharing selection and maintenance essentials for the GICL series.