A unit for a ring spinning machine is a part of a compaction device for compressing a fiber composite (9) by means of a suction tube (8) downstream of a drafting device. The unit has a transmission housing used for accommodating a speed changer and two parallel axles. Each axle has two ends which projection from the transmission housing on opposite sides and extend from the transmission housing, upper rollers are rotatably fixed on the end parts, and each upper roller is provided with a driving element. The drive elements (18) of two upper rollers (4, 5) of one side of the transmission housing (13) are connected to one another by means of a transmission element (19). The transmission housing (13) has an upper and a lower side (24, 25) and does not project beyond all common tangent planes (T1, T2) of these upper rollers (4, 5) in a region between the upper rollers (4, 5). Both the upper and lower side (24, 25) have a distance from these tangent planes (T1, T2), so that the upper or lower side (24, 25) facing the suction tube (8) of the unit do not contact the suction tube (8).