referring now in detail to the drawings , the reference numeral 10 denotes generally a mold assembly constructed in accordance with and embodying the invention . the mold assembly 10 may comprise a mold base assembly fabricated of standardized components such as available from d . m . e . corporation of detroit , mich . and generally known in the industry . as such , various commonly employed components which are not essential to an understanding of the invention , such as ejector pins , ejector retainer plates , ejector plates and ejector housings have been omitted to more clearly illustrate the invention . it should also be understood that although depicted in conjunction with a vertical mold assembly , the invention has equal applicability in horizontal or front - to - back mold assemblies . the mold assembly 10 includes a mold cavity 12 configured for molding a plastic wheel cover having a mounting system substantially as disclosed in u . s . pat . no . 3 , 876 , 257 , incorporated herein by reference . such wheel cover includes an annular channel formed in a collar which projects axially from its inner face . an annular grip ring is seated in the channel . the mold assembly 10 includes an upper base 14 , formed of a top clamping plate 16 and a mold cavity plate 18 . the mold assembly 10 also includes a lower base 20 , formed of a support plate 22 , a core retainer plate 24 and a mold core plate 26 . it should be appreciated that an ejector assembly ( not shown ) may be positioned beneath the support plate 22 as is conventional . the mold cavity plate 18 includes mold cavity surfaces 28 which define portions of the mold cavity 12 for shaping the axially outer face of the wheel cover . similarly , the mold core plate 26 includes mold cavity surfaces 30 , which serve to configure the inner face of the wheel cover . pursuant to the invention , a segment of the core retainer plate 24 includes mounting system mold components comprising a cylindrical wall 32 , which defines the mold cavity surface for the radially outer face of a collar in which a channel is formed and an adjacent surface 34 which defines the mold cavity surface for a peripheral lip on the inner face of the wheel cover . an annular mold insert 36 is also seated against a lower portion of the wall 32 . the mold insert 36 is configured with a reduced thickness cylindrical band 38 which defines mold cavity surfaces for the grip ring channel of the wheel cover . it should also be noted that the mold core 26 is received in the core retainer plate 24 and includes a peripheral cylindrical wall 38 which defines the mold cavity surface for radially inner face of the collar . in accordance with the invention , the top clamping plate 16 , the core retainer plate 24 , the insert 36 and the support plate 22 constitute multiple use common molding system components which are employed for molding differently styled wheel covers for the same size wheel . for example , illustrated in fig2 is a mold assembly 10a for molding a wheel cover having a plurality of vent openings and with a different contour than the wheel cover molded with the mold cavity 12 of the mold assembly 10 illustrated in fig1 . the mold assembly 10a depicted in fig2 utilizes the same top clamping plate 16 , core retainer plate 24 , mold insert 36 and mold support 22 as the mold assembly depicted in fig1 . only the mold components which define the aesthetic configuration of the wheel cover , i . e . a mold cavity plate 18a and a mold core plate 26a have been changed . in fig3 there is depicted a mold assembly 40 configured for molding a plastic wheel cover having a mounting system comprising a plurality of clips seated in sockets formed on the inner face of a wheel cover . a typical example of such mounting system is disclosed in u . s . pat . no . 4 , 523 , 789 , incorporated herein by reference . the mold assembly 40 is configured with a mold cavity 42 defining the desired wheel cover shape and includes an upper base 44 , formed of a top clamping plate 46 and a mold cavity plate 48 . the mold assembly 40 also includes a lower base 50 formed of a support plate 52 , a core retainer plate 54 and a mold core plate 56 . as will be noted from an examination of fig4 comprising a sectional view taken through an alternate radial plane wherein the molded wheel cover will not include a retention socket , the core retainer plate 54 is formed substantially of one piece construction . the mold cavity plate 48 includes mold cavity surfaces 58 which define portions of the mold cavity 42 for shaping the axially outer face of the wheel cover . similarly , the mold core plate 56 includes mold cavity surfaces 60 which serve to configure the inner face of the wheel cover . pursuant to the invention , the core retainer plate 54 includes a central recessed well having a generally flat planar circular central area defined by an annular shoulder 62 . from the top of the shoulder 62 , the core retainer plate extends radially outwardly along a planar surface 64 , the outer circumference of which is defined by an annular wall 66 . a first spacer insert ring 68 of substantially rectangular cross section is seated against the shoulder 62 and its radially inner surface defines a shoulder against which the mold core plate 56 is seated as depicted in fig4 . a second insert ring 70 is seated on top of the first insert ring 68 and on the planar surface 64 and is positioned between the mold core plate 56 and the planar wall 66 . as will be seen from an examination of fig4 in areas of the wheel cover wherein no retention clip sockets are provided , the mold core surface 60 of the mold core plate 56 is continuous with the upper surface of the second insert ring 70 to provide a smooth inner face for the wheel cover . in equidistantly spaced areas around a circle , the core retainer plate 54 includes a hollow seat or well 72 . within each well 72 , a mold insert 74 is seated . the mold inserts 74 include a substantially rectangular upwardly projecting tongue which serves to define the mold cavity surfaces for a seat area of a socket for receiving a wheel retention clip . mold cavity surfaces for the radially inner wall of each socket , as well as the sides of each socket are formed by cut away portions of the core retainer plate 54 , while mold cavity surfaces for the outer wall of each socket which includes a wheel cover centering rib which projects radially outwardly from each socket , is formed by a cut away portion of the second insert ring 70 . to produce a differently styled wheel cover having the same retention system utilizing the mold assembly 40 , one need only substitute a new mold cavity plate and a new mold core plate which have mold cavity surfaces configured for the differently styled wheel cover . with attention now directed to fig5 wherein a fragmentary portion of a wheel cover having a spring wire band retention system is disclosed , it should be noted that the retention system disclosed therein includes a pair of spaced mounting legs having a radially outwardly projecting boss designed to engage the draw bead step in a wheel rim , with the legs being outwardly biased by the wire band . a central leg bears against the wire band and serves to maintain the band in position seated in a groove on the inner face of the mounting legs . wheel covers having retention systems of this general configuration are disclosed in u . s . pat . nos . 4 , 822 , 102 and 3 , 480 , 329 , both of which are incorporated herein by reference . a mold assembly 80 is configured to mold a plastic wheel cover in the shape of a mold cavity 82 having the retention system depicted in fig5 and includes an upper base 84 formed of a top clamping plate 86 and a mold cavity plate 88 . the mold assembly 80 also includes a lower base 90 formed of a support plate 92 , a core retainer plate 94 and a mold core plate 96 . as with the mold assemblies 10 and 40 , a conventional ejector assembly ( not shown ) may be positioned beneath the mold support plate with ejector pins extending through the support plate , the core retainer plate and the mold core plate . the mold cavity plate 88 includes mold cavity surfaces 98 which define portions of the mold cavity for shaping the outer face of the wheel cover . similarly , the mold core plate 96 includes mold cavity surfaces 100 which serve to configure the inner face of the wheel cover . pursuant to the invention , the core retainer plate 94 includes an annular planar surface against which the mold core plate is seated . in equidistantly spaced selected areas along the periphery of the planar seat surface , the core retainer plate extends about a curved surface downwardly to define a mold cavity surface for the groove on the inner face of the mounting leg . mold cavity surfaces for the radially outer surface of the mounting legs , as well as a registered corresponding zone 102 on the inner face of the wheel cover , are defined by surfaces of a core insert 104 which is secured to a cam block 106 . the juncture of the mold core insert inner wheel cover face mold cavity surface and the surrounding mold cavity surface of the mold core plate 96 appears as a line 107 on the inner wheel cover face . the cam block 106 moves in a radially outward direction when the upper base 84 is separated from the lower base 90 as a result of engagement between a cam 108 , secured in the cavity plate 88 and a mating cam surface of the cam block 106 . such cam structures are well known to those familiar with conventional molding techniques . tables of active cam distances for pulling cores are readily available from sources such as d . m . e . corporation of detroit , mich ., e . g . d . m . e . catalog , copyright 1966 , p 264 , data sheet no . 101 incorporated herein by reference . in accordance with the invention , in instances wherein a different configuration plastic wheel cover is to be molded with the same retention system , only the cavity plate 88 and the core plate 96 need be modified to provide mold cavity surfaces defining the new wheel cover configuration . with reference now to fig7 wherein a flow chart depicting the various steps in the method of the present invention is illustrated , it will be seen that in accordance with the molding system , a mold assembly for a wheel cover having a specified mounting system is assembled by tooling the mounting system components common to all differently styled wheel covers having the same mounting system and wheel size as depicted in a block 110 . additionally , the mold cavity plate for the first style wheel cover is tooled as depicted in a block 112 and the mating mold core plate for the first styled wheel cover is tooled as depicted in a block 114 . the tooling steps depicted in the blocks 110 , 112 and 114 may take place simultaneously or sequentially . when the styling configuration of additional wheel covers is known , the steps of tooling the mold cavity for the next and subsequent styled wheel covers proceeds as indicated in a series of blocks 116 , 118 and 120 . the steps of tooling the mating mold core plates for the next styled wheel covers as depicted in blocks 122 , 124 and 126 also proceeds . the steps of tooling for subsequent styled wheel covers as depicted in blocks 116 through 126 may take place at any time . after the tooling has been completed for the mounting system components and for the mold cavity plate and mold core plate for the first styled wheel cover , the step of assembling the composite mold assembly , as indicated in a block 128 , takes place . thereafter , a production run is commenced as indicated in a block 130 . after completion of the production run , the method proceeds to the step of disassembling the composite mold assembly while retaining the common mounting system components . after disassembly , as indicated in a block 132 , the mold cavity plate and the mold core plate are stored as indicated in a pair of blocks 134 and 136 , respectively . when it is appropriate to commence production of the next styled wheel cover having the same mounting system , the appropriate mold cavity plate and mold core plate which were tooled in the steps 116 and 122 , for example , are utilized to assemble the composite mold assembly for the next styled wheel cover , utilizing the retained mounting system components , as indicated in a block 138 . thereafter , the method returns to the commencement of a production run as indicated in the block 130 . after the production run has been completed , the method proceeds through the steps indicated in the blocks 132 , 134 and 136 and returns to the block 138 , however utilizing the appropriately styled mold cavity plates and mold core plates tooled in the steps 118 and 124 , respectively . additional mold cavity plates and mold core plates for further differently styled wheel covers such as those tooled in the steps 120 and 126 and any further mold cavity and mold core tooling steps may be utilized to assemble composite mold assemblies as may be required for further differently styled wheel covers or , should the occasion arise for subsequent production runs of previously molded wheel cover styles , any previously used mold cavity plate and mold core plate sets stored in the steps indicated in the blocks 134 and 136 may be reemployed . thus it will be seen that there is provided a system and method for molding plastic wheel covers which achieves the various aspects , features and considerations of the present invention and which is well adapted to meet the conditions of practical usage . as various changes might be made in the illustrative embodiments herein disclosed without departing from the spirit of the invention , it is to be understood that all matter herein described or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense .