A small-sized submersible pump unit having a submersible motor, discharge module, pump housings which are connected by flangeless coupling is disclosed. The flangeless coupling is made using embedded ring segments. The coupled housings each have the covering and the covered parts, and the covered part of one of the housings contains a blind rectangle groove, and the covering part of another housing has a through rectangle groove, and the grooves form a cavity having an embedded ring segment.