disposed on the inside of a refining disc and which is intended for coaction with the same or different kind of refining segments on an adjacent refining disc on the other side of the refining gap several segments as shown in fig2 are typically secured side by side to a base e g rotor or stator to form a substantially circular e g circular or annular refining plate the segment has the general shape of a truncated sector of a circle each segment may be mounted to the plate holder surface of the base by means of machine screws inserted through countered bolt holes 56 some refiner designs may allow fastening the plates from the back which eliminates the bolt holes from the face of the plate in general segments are mounted on discs rotating relative to each other which could be achieved by the presence of one rotor and one stator single disc refiner or by one rotor segmented on both sides and operating against two stators double disc refiner or by several rotors working against each other and a pair of stators multi disc refiner or by counter rotating discs each refining disc segment can be considered as having a radially inner end 58 a radially outer end 60 and a working surface therebetween the working surface including a plurality of bars 62 laterally spaced by intervening grooves and extending generally outwardly toward the outer end across the surface preferably all but at least most of the bars are curved with the shape of a logarithmic spiral as is common for both low and high consistency refining of wood chip or second stage material the bars.