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. 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.