referring to fig1 , 2 and 3 , views are shown to improved wheels 2 and 3 that are fitted with an axle retainer assembly 4 . the wheels 2 and 3 are constructed from blow - molded plastic wheels 6 and 7 . the wheels 6 and 7 each include a cavity 8 that receives an axle retainer assembly 4 . a double - ended pin 10 of the assembly 4 aligns with and mounts to an annular groove 12 of an axle 14 , reference fig3 . the wheels 6 and 7 are blow - molded in conventional fashion and provide a hub 16 and from which a number of spokes 18 and intermediate flat webs 19 radiate to an annular box or rim 20 . the wheel 6 includes a number of lugged treads 22 . the treads 22 are molded into a tread surface 24 that engages the ground . a raised band 26 projects around the circumference of the wheel 6 and above the treads 22 at the center of the tread surface 24 . a parting line defined by the molding operation extends around the center of the band 26 . an accessory trim piece or whitewall 28 can be attached to an annular grove 30 that is formed into one or both exposed side wall faces of the box 20 . the blow - molded wheel 3 of fig2 is substantially the same as the wheel 2 , except a separately molded tread piece 5 is mounted to the box 20 . a smooth , recessed surface 7 a of the box 20 includes a flange 9 and to which the tread piece 5 is aligned . the tread piece 5 is molded from an ethylene methyl acrylate ( ema ) copolymer , although an eea , eva or lldpe material , among other materials could be used . a number of lugged treads 11 are molded into the tread piece 5 . the tread piece 5 is stretch fitted over the wheel 7 while warm . the density of the tread piece 5 is selected to provide a durable , long - wearing surface . the tread piece 5 also minimizes rolling sounds of the wheel 3 over certain surfaces and which sounds otherwise can be magnified due to the hollow cavity at the wheel 3 . returning attention to fig1 , the cavity 8 is molded into one of the spokes 18 . the cavity 8 opens at one end into a body bore 29 . an opposite end provides a closed wall 33 . a housing 31 of the assembly 4 includes a pin sleeve 32 that mounts within the cavity 8 . the pin 10 is supported within a bore 34 of the pin sleeve 32 and is biased to permit reciprocating movement in conjunction with a spring 36 . the pin 10 projects through an aperture 38 of the bore 34 , reference fig3 , and into a longitudinal bore 40 of an axle sleeve 42 that extends transverse to the pin sleeve 32 . the spring 36 abuts an end of the recess 33 at an open end of the pin sleeve 32 . the bore 40 separately accepts the axle 14 . the bore 40 provides a load - bearing surface for the axle 14 . a cover 46 closes the end of the housing 31 and bole 40 . the housing 31 is retained to the wheel 6 at the pin and axle sleeves 32 and 42 . the transverse orientation of the pin and axle sleeves 32 and 42 to one another assures that the retainer assembly 4 does not loosen and rotate with the wheel 6 . the retainer housing 31 can be bonded to the wheel 6 . presently it is secured through the shrinkage of the wheel material . if required , retention can be enhanced by forming the external walls of the retainer to include shaped surfaces such as described below in relation to fig6 and 7 . with additional attention to fig3 and 4 , an aperture 48 extends through a side wall of the axle sleeve 42 and is exposed at the wheel 6 to permit access to the pin 10 . by inserting a tool through the aperture 48 , a shoulder 47 of the pin 10 can be engaged and the pin 10 can be depressed to release one of a pair of ends 49 from the axle 14 . the aperture 48 can be flashed over , such as in fig2 , when molding the housing 31 to prevent casual access to the pin 10 . depending upon the application , the wheels 6 and 7 can be molded from a variety of types of plastic . the type of plastic and density of material can be varied to a particular application and the load and wear specifications for a particular wheel . the configuration and size of the wheels 6 and 7 can also be varied . the wheels 6 and 7 are presently molded from a high - density polyethylene material and each is constructed to a 12 - inch diameter . a variety of other known materials can be used to equal advantage . the retainer housing 31 is molded from a material that is compatible to the wheel material . an hdpe material is presently used . depending on the application , however , the housing 31 can be constructed from a variety of other materials including various metals and plastics . the pin 10 is constructed from metal . various other materials can be used provided they are able to withstand anticipated wear at the axle 14 . after extracting the wheel 6 from its mold and while the plastic is warm , the retainer assembly 4 is fitted to the cavity 8 and the bore 31 . as the wheel 6 cools , the material shrinks around the axle sleeves 32 and 42 to permanently mount the retainer assembly 4 to the wheel 6 . although not presently required , the retention might be enhanced by shaping the external surfaces of the sleeves 32 and 42 to grip mating surfaces of the wheels 6 and 7 . for example and with additional attention to fig6 , a flat surface 50 and / or raised projections 52 and / or one or more recesses 54 can be provided . presently , a recessed groove 54 is included . the groove 54 separately aids in the extraction of the retainer housing 31 from an injection mold . the raised projections 52 can be formed as annular ribs or knurling . fig7 and 8 depict a front and rear view to a wheel 60 that is fitted with a retainer housing 62 . the housing 62 supports a retainer pin and spring at a pin sleeve 63 in a fashion similar to the retainer assembly 4 . a bore 65 ( shown in dashed line ) through an axle sleeve 67 supports an axle 14 . a groove 64 extends around the exterior of the housing 62 . separately formed into the housing 62 are a groove 66 and raised projection 68 that extend approximately one - half the circumference of the housing 62 . also shown in dashed line is a raised band 70 that can be included or not and that can have a rounded exposed surface , like an o &# 39 ; ring , or a wedge or ramped shape . appropriate provisioning of the exterior surface of the housing 62 with grooves 64 , 66 and / or projections 68 and 70 facilitates retention of the housing in the wheel 60 . fig9 through 12 show wheels 90 and 92 that are molded with integral retainer sleeves 95 and 96 . such a construction avoids the necessity of fitting a separate retainer housing to a finished wheel . the sleeves , however , require additional plastic and can increase the complexity of the mold and / or molding difficulty . the sleeves 95 and 96 extend from the hub 16 to the box 20 of the wheels 90 and 92 along webs 98 and 100 . the webs 98 and 100 are vertically offset from the other webs 19 . the sleeve 96 exhibits a larger outer diameter than the sleeve 95 and tapers inward slightly as it extends to the box 20 . the sleeves 95 and 96 include longitudinal bores 95 and 97 that receive an appropriate retainer pin and spring . the bores 94 and 97 are accessed by drilling aligned holes 101 and 103 through the periphery of the box 20 and hub 16 . the drilling operation is typically performed after molding the wheels 90 and 92 . the tread piece 5 and / or a plug ( not shown ) cover and / or fill the holes 101 and 103 . fig1 through 18 depict front and rear views of wheels 102 , 104 and 106 that include retainer sleeves 108 , 110 and 112 that are molded to avoid having to drill holes through the box 20 to facilitate mounting an axle retainer pin and / or spring . the retainer sleeves 108 , 110 and 112 are molded into webs 114 , 116 and 118 that are elevated above the webs 19 between the other spokes 18 . the elevation of the webs 114 , 116 and 118 is determined relative to the necessary boring operations . the web 118 also includes a slight recess 119 that is visible at fig1 . aligned grooves 120 , 122 and 124 are molded into the box 20 of the wheels 102 , 104 and 106 to facilitate forming the bores 126 , 128 and 130 of the retainer sleeves 108 , 110 and 112 . the grooves 120 , 122 and 124 are shown exposed , although are normally substantially covered by the tread piece 5 . the bores 128 and 130 are formed with two differing internal diameters that define an internal shoulder that limits the movement of the retainer pin . upon fitting an appropriate retainer pin and bias spring mechanism into the retainer sleeves 94 , 96 , 108 , 110 and 112 , an end cap is secured to the sleeves . a threaded end cap is typically used , although , a variety of other plugs can be substituted , provided they securely retain the retainer pin in the pin sleeve . two other alternative wheels 132 and 134 are shown in fig1 through 22 . the wheels 132 and 134 include retainer sleeves 136 and 138 that extend at acute angles relative to a plane that contains the parting line of each wheel . the sleeves extend along webs 140 and 142 . the web 140 extends from the hub 16 at a continuous slope . the web 142 , in contrast , provides an elevated interior portion 144 that is raised above an outer portion 146 . bores 148 and 150 extend through the sleeves 136 and 138 . upon drilling the sleeves 136 and 138 , fitting appropriate retainer pins and springs , a threaded end cap 152 is secured to each sleeve 136 and 138 . fig2 lastly depicts a cross section view to the mounting of an alternative tread piece 160 to a blow - molded wheel 162 . the wheel 162 is essentially similar to the wheel 3 , except that it includes a raised projection 164 at the parting line of the wheel 162 . the wheel 162 can be adapted to include any of the foregoing axle retainers or not , as desired . the projection 164 mounts within a slot 166 molded into the tread piece 160 . the mating of the slot 166 to the projection 164 stabilizes the tread piece 160 against lateral slippage and minimizes possible tread separation . in most instances , the annular flanges 9 are sufficient to prevent tread separation . although a single , continuous projection 164 is shown , multiple adjacent projections 164 can be provided at the periphery of the blow - molded wheel 162 . the projections 164 can also be constructed to be discontinuous . the projections can exhibit rounded , ramped , or other contour shapes , when viewed in side profile , such as the projections 52 and 68 . while the invention has been described with respect to a preferred construction and considered improvements or alternatives thereto , still other constructions may be suggested to those skilled in the art . although certain features are also shown at particular wheels , it is also to be appreciated the features can be included alone or in other combinations in other of the disclosed wheels . the foregoing description should therefore be construed to include all those embodiments within the spirit and scope of the following claims .