referring to the figures , there is shown a valve assembly 10 which comprises a body 11 and stem 12 . the body 11 is conveniently formed from extruded hexagonal bar stock of brass or other corrosion - resistant material . at a rearward end of the body 11 , the original stock surfaces are left to provide wrenching flats 13 , while at the forward end of the body , these surfaces are machined or otherwise displaced to provide external pipe threads 14 for mounting the body 11 on a fluid - containing vessel . the body 11 is provided with a through bore comprising an area of internal threads 17 at the rearward end of the body and a counterbore 18 at the forward body end . a radial end face 19 of the body 11 intercepts counterbore 18 to form an annular seat or edge 20 . the stem 12 comprises integral handle , threaded , and head portions 23 , 24 , and 25 , respectively . like the body 11 , the stem 12 is advantageously formed of corrosion - resistant material such as brass . the stem 12 is conveniently fabricated from a blank cut from a t - shaped extrusion by machining or otherwise forming threads 26 on the elongated threaded portion 24 and forming outer surfaces 27 , 27a of the head portion 25 by relative rotation about a longitudinal axis 21 of the stem . as shown , the handle portion 23 has a transverse length substantially greater than the diameter of its internal body threads 17 , and , preferably , greater than the transverse diemsions of the body 11 to permit the stem to be readily gripped and operated by the fingers of a mechanic . a blind axial pilot bore 31 extends axially along the stem 12 substantially the full length of the head portion 25 so that the head portion is tubular substantially alongs its full length . that is , an imaginary plane transverse to the axis 21 of the stem would intercept both the outer head surfaces 27 , 27a and the interior surface defined by the blind bore 31 anywhere along the major portion of the head length . an axial passage or bore 34 is drilled otherwise formed through the handle and threaded portions 23 , 24 of the stem 12 . the passage 34 communicates between an end face 36 of the handle and a diametral passage or cross bore 35 drilled or otherwise formed through an area of the stem 12 between the threaded portion 24 and head portion 25 . prior to the assembly of the stem 12 into the body 11 , the stem head portion 25 is substantially cylindrical , having an outer diameter corresponding to the surface 27 and at least as small as the minor diameter of the internal threads 17 of the body , so that the stem 12 is enabled to be screwed into the body head first from the rearward end of the body axially forward to the position illustrated in fig2 . a tool 32 , illustrated in phantom in the form of a conical ram , is forcibly driven into the bore 31 to plastically expand or flare the head portion 25 radially outwardly to the condition illustrated in fig1 and 2 where its major diameter , designated 33 , is somewhat larger than the body seat 20 . this flaring of the head portion 25 provides the conical outer sealing surface 27a , increasing in diameter in a direction away from the handle portion 23 , adapted to sealingly engage the annular body seat 20 in an axial zone adjacent an outer end face 37 of the stem 12 , as illustrated in fig1 . the disclosed structure of the valve assembly 10 is particularly suited for use as a draincock in an automotive cooling system . as is customary , the body 11 is screwed into a bushing or other threaded port on a radiator or other fluid containing vessel near its lower end to permit the vessel to be drained . normally , the valve assembly 10 is closed by backing the stem 12 out to the position illustrated in fig2 where the stem surface 27a , sealingly engages the annular seat 20 . fluid pressure on the outer end face 37 and the bore 31 of the head portion 25 tends to advantageously increase the sealing pressure on the seat 20 during service . this increased sealing action and the initial seating of the surface 27a against the seat 20 are facilitated by the tubular structure of the head , which provides a certain amount of resiliency in the head structure to accommodate misalignment or eccentricity between the body 11 and stem 12 . it may be seen that sedimentary accumulations in the area of the surface 27a and the seat 20 are readily broken free as the stem 12 is screwed into the body 11 from the position illustrated in fig1 to that illustrated in fig2 . in the open position of the stem 12 , fluid passes into the cross passage 35 and then through the axial stem passage 34 , rearwardly exiting at the handle portion 23 . it may be appreciated that the structure of the disclosed valve assembly 10 comprises a minimum of two parts , thereby offering reduced manufacturing cost . further , once the head portion 25 is flared or expanded radially , as described , the assembly may not be mistakenly or inadvertently disassembled , since neither the handle nor expanded head portions 23 , 24 will pass through the body . while the above description discloses the use of brass to form both the body 11 and stem 12 , it is deemed within the scope of the invention that these parts be formed of other materials , with the parts of an assembly being formed of similar or dissimilar materials . for example , both the body 11 and stem 12 , or merely the stem , may be formed of a plastic such as nylon , in which case the head portion of the stem may be flared while it is at an elevated temperature to permit it to be plastically deformed in the desired manner . of course , the parts 11 and 12 may be made of steel , and may be coated or treated to provide corrosion - resistance for service in corrosive environments . it is also contemplated that rather than plastically flaring the stem head portion 25 radially outwardly from an initial cylindrical configuration , the stem may be molded or otherwise formed in situ in the body 11 . while i have described my invention in connection with a specific embodiment thereof , it is to be clearly understood that this is done only by way of example , and not as a limitation to the scope of my invention as set forth in the objects thereof and in the appended claims .