A
piston assembly (10) for a flowable materials container having a
barrel (14) defining a fluid containing chamber (16). The
barrel (14) is made of a body of a cyclic olefin containing
polymer or a bridged polycyclic olefin containing
polymer. An elastomeric
piston (24) is slidably attached to the
barrel (14) and provides a seal of the chamber. The
piston (24) has a
parylene coating on an outer surface thereof to reduce the necessary break away force. A
plunger (22) is also provided and has a second
mating member (42) removably connecting the
plunger to a first
mating member (44) of the piston. The first
mating member (44) has a series of threads having a major
diameter and a minor
diameter, and the second mating member (42) has a series of threads having a major
diameter and a minor diameter. The
major and minor diameters of the second mating members (42) is appreciably smaller than the
major and minor diameters of the other of the first mating member (44) to provide ease of connection.