A seat (10), the frame of whose backrest (11) and/or seat part (12) includes at least two tubes (21a, 21 b, 22a, 22b) or bars, in connection with which structural parts (30), which have holes (32) for the tubes of the frame of the backrest and/or the frame of the seat part, can be installed. The structural part has, in connection with the hole, a shoulder (33) on which the bushing (34) of the adjacent structural part rests so that a gap remains between the structural parts. Most advantageously, the structural part has been made of plastic, and there can be a padding (35) on top of it.