A device for connecting operating units (8) for doors and windows comprising: a control element (4) mounted on the operating side (3 a) of a mobile frame (3); a rod segment (5) that is slidably mounted in a groove (C), made at least in the operating side (3a) and is connected to the control element (4) in such a way as to slide in both directions within the groove (C) to define the open and closed configurations of the door/window (1a, 1b); the rod segment (5) being associated by respective connecting means (10, 12), with elements (105, 6) that are functional or accessory to the operation of the rod segment (5), said elements (105, 6) protruding from the groove (C); these connecting means comprise at least one base (10) connected to at least one functional or accessory element (105, 6) defined by an operative portion (9); the size of the base (10) is such that, in use, it covers a free front section of the rod segment (5), the base (10) being frontally applicable to the rod segment (5) before the latter is inserted into the groove (C), and a bottom end extension (12) protruding transversally of the base (10), shaped to match the profile of the operating rod segment (5) and designed to be coupled to a respective slot (5a) formed on the rod (5) in such a way as to create a portion for uninterruptedly connecting and stiffening the rod segment (5) itself.