transducer - protector device for biomedical haemodialysis lines comprising a first and a second element each of which is formed in a single piece of moulded plastic material with a tubular fitting and an annular radial flange . the first element is formed with a semi - crystalline polymer and the related annular radial flange has greatly thinner portions able to allow the see - through viewing of the filtering membrane secured between the flanges of the first and of the second element .