These numbers (such as 3.5 mm, 3.81 mm, 5.0 mm, 5.08 mm, 7.5 mm, 7.62 mm) represent different spacing and are commonly used to describe the size of PCB terminal blocks. Here are some differences and common uses between them: Ningbo HongYi Electronic Ltd Co. 3.5mm terminal blocks Ningbo HongYi Electronic Ltd Co. Ningbo HongYi Electronic Ltd Co. 7.5mm terminal blocks These wiring terminals with different spacing have their respective applicable application ranges, and the choice of suitable spacing depends on specific application requirements, such as power requirements, space limitations, and electrical characteristics. When choosing, it is necessary to consider the actual situation and design requirements comprehensively.