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. Overall, Japan, the US and Europe each have their strengths in crowned tooth and gear couplings: Japan excels in tooth crowning and consistency, the US in high-torque grading and durability, and Europe in integrated design and sealing. The domestic GICL series, however, holds clear advantages in cost-performance, lead time and spare-part convenience, meeting most medium-to-heavy duty conditions. 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.