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. In Japan, gear and crowned tooth couplings mostly follow standards such as JIS B 1452, with representative manufacturers including Sumitomo Heavy Industries and NTN. Their products emphasize modular design and high consistency, and are mature in precision transmission. Compared with domestic GICL series, Japanese products have richer experience in tooth crowning, noise control and batch stability, but purchase price and lead time are usually higher. 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.