22 b between the second feeding element 22 b and the central sleeve 26 between the central sleeve 26 and the first feeding element 22 a and between the first feeding element 22 a and the mixer shaft 42 the 0 rings provide for a snug fit between the components that remains tight during operation and further serve to prevent material from entering seams and crevices in the components the central sleeve 26 can optionally be formed slightly shorter in length than the space between the feeding elements 22 relying on the compression of the o rings to ensure a tight seal the mixing chamber screen 24 is thus clamped tightly between the first and second feeding elements 22 a 22 b 0023 fig2 a 2b and 2 c are top views of various feeding elements 22 in accordance with the present invention the feeding elements 22 comprise an annular body 44 having a plurality of openings 46 formed at acute angles for example 30 45 degrees relative to the longitudinal axis 48 see fig1 a of the mixer head 20 the openings are preferably circular in cross section for ease of manufacture other shapes are equally applicable the feeding elements further include a circular recess 50 adapted for receiving an o ring 40 the first and second feeding elements 22.