ST Series I/O Connectors The Hirose Electric ST Series I/O Connectors were developed as external input/output connectors for portable and mobile devices. The connectors assure reliable electrical and mechanical performance under extreme and unpredictable conditions. The Hirose ST Series I/O Connectors feature a solid locking system for strong mating strength, a 4-keying structure to prevent upside down insertion, and a lot of varieties to support various kinds of connections with peripheral equipment.