The present invention relates to a fluid cassette, e.g. a blood treatment cassette (1000) comprising a cassette body, which is designed as a hard part (1), and optionally a film (3), which is connected to the hard part (1) and covers the hard part (1) at least in sections thereof, the hard part (1) comprising at least a first centering device (504) and a second centering device (505) which are optionally arranged on or associated with opposite first and second sides of the fluid cassette (1000). The invention further relates to a blood treatment device.
