passageway 34 when in the retracted position which minimizes any obstruction to the flow of thermoplastic material to the discharge passageway 44 the cleaning probe 56 is characterized by a diameter measured radially relative to its length typically the diameter of cleaning probe 56 is uniform along its length although the invention is not so limited the diameter of the cleaning probe 56 is slightly less than a diameter of the discharge passageway 44 measured radially relative to the longitudinal axis 38 to the cylindrical inwardly facing surface surrounding passageway 44 the dimensional difference provides a clearance sufficient for the leading tip 53 of cleaning probe 56 to enter and extend through the discharge passageway 44 the cleaning probe 56 may be for example formed from a short length of wire or rod the leading tip 53 may be blunt as shown in fig1 u2013 3 or may have a different configuration such as tapering to a point an external threaded portion 58 of cleaning fixture 50 is engaged with an internal threaded portion 60 of a bushing 52 sealingly engaged with passageway 40 bushing 52 is fixed within body 24 in a suitable manner such as by brazing the mated threaded portions 58 60 cooperate for guiding the cleaning probe 56 axially along longitudinal axis 38 toward the discharge passageway 44 a rotating driving element 54 is used to apply a torque for turning threaded portion 58 relative to stationary threaded portion 60 in one rotational direction to advance the cleaning probe 56 from the retracted position to the extended position to withdraw the cleaning probe 56 from the.