This document specifies the structure and specifications, basic requirements, technical requirements, test methods, inspection rules, marking, packaging, transportation, storage and quality commitment of plug-in external rotor volute-less fans (hereinafter referred to as fans). This document is suitable for use in data centers, powered by AC single or three-phase power, with an input power not greater than 10 kW, and a plug-in external rotor volute-less fan driven by an electronically commutated permanent magnet synchronous motor. Other similar products can be used as a reference.