Crowned tooth couplings replace straight teeth with crowned teeth, distributing meshing contact more evenly along the tooth width and thereby improving load capacity and fatigue life. Domestic products follow GB/T crowned tooth coupling standards, differing from foreign products in structure and parameter systems. 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.