by reference now to fig1 through 9 , there is illustrated a preferred embodiment of a disposable finishing article drive member assembly constructed in accordance with the principles of the present invention . the finishing article constructed in accordance with the present invention may take many forms , such , for example , as grinding wheels , flap wheels , wire wheels , abrasive disks or pads , buffs or the like . for purposes of ease of illustration and clarity of description only a depressed center grinding wheel will be shown and described . it will , however , be understood by those skilled in the art that other disposable finishing articles which may be placed in compression during use thereof may be substituted for the grinding wheel without departing from the spirit or scope of the present invention . as is shown in fig1 through 6 , a depressed center grinding wheel 10 has a disposable drive member or hub assembly 12 permanently affixed thereto without the use of adhesives so that the grinding wheel may be attached to the threaded spindle 14 of an appropriate power tool 16 ( only partially illustrated ). according to the principles of the present invention , a disposable mounting hub or drive member is constructed in such a manner that when the grinding wheel is placed in operation upon the spindle 14 the grinding wheel 10 is placed in compression and the more force that is applied to the grinding wheel during utilization thereof , the greater the operational compression becomes . as a result of placing the grinding wheel in such compression the grinding wheel is maintained upon the spindle and at the same time , through the compression or clamping force , the grinding wheel 10 cannot rotate relative to the drive member or hub assembly 12 . however , as a result of the construction of the drive member , the spent grinding wheel may be easily removed from the spindle for disposal without the utilization of hand tools or the like . as is clearly shown , the grinding wheel 10 includes a back surface 18 and a front surface 20 . the central portion of the grinding wheel is depressed as viewed from the front thereof and as is shown at 22 , with a corresponding central raised portion 24 on the back thereof . a centrally located aperture 26 is provided in the depressed center portion of the grinding wheel 10 . the purpose of the depressed center of the grinding wheel 10 is to insure that the driving member or spindle does not protrude beyond the face portion 20 of the wheel 10 and thus interfere with a workpiece during the time the grinding wheel 10 is being utilized . however , when certain types of finishing articles are utilized such that the outer circumference or face is used instead of the entire face , then a depressed center may not be included in the article . a backing flange 28 is provided and is adapted to be snugly received on the back surface 18 of the grinding wheel 10 about the raised portion 24 . the flange 28 has a diameter which is less than the diameter of the wheel 10 . the backing flange 28 defines a second central aperture 30 therethrough which is aligned with the aperture 26 in the grinding wheel 10 . circular reinforcing ribs 32 and 34 ar formed in the backing flange 28 concentrically with the opening 30 . radial reinforcing ribs 33 are formed intersecting the concentric ribs 32 and 34 . it has been found that the use of the radial ribs 33 on the backing flange 28 provides unexpected stiffness . such stiffness is desired in certain applications of grinding wheels where large amounts of pressure are applied to the wheel during grinding . the backing flange 28 is preferably stamped from sheet metal but of course could be constructed from other materials such as hard molded plastic or die cast metal should such be desired . as is shown more specifically in fig3 the backing flange 28 includes an inner surface 36 and an outer surface 38 . the inner surface 36 is disposed opposed the back surface 18 of the abrasive finishing wheel 10 . the inner surface 36 includes a land 40 . the land 40 is formed about the outer peripheral portion of the backing flange 28 . the land 40 always engages the back surface 18 of the abrasive finishing wheel away from the depressed center . in addition , a broken land 42 is formed by the inner surface 36 between the radial reinforcing ribs 33 . the land 42 may engage the back surface of the abrasive finishing wheel 10 opposed the depressed center 22 thereof depending upon variations in wheel dimensions and manufacturing tolerances in the wheels and flanges . as can be seen , particularly in fig3 the ribs 32 and 34 formed in the outer surface 38 of the backing flange 22 are continuous . the continuous rib 32 is disposed between the lands 40 and 42 and over the transitional area between the depressed center and the remainder of the grinding wheel 10 while the continuous rib 34 is disposed intermediate the opening 30 and the land 42 . selected ones of the radial reinforcing ribs 33 have radially inwardly directed fingers 35 , 37 , 39 and 41 formed therein . preferably , when the backing flange 28 is fabricated from stamped sheet metal the fingers 35 , 37 , 39 and 41 may be formed by cutting or punching the sheet metal during the stamping operation . when the fingers are formed a space is provided beneath the distal end 92 , 94 , 96 and 98 as shown at 100 , 102 , 104 and 106 respectively . the purpose and function of the gripping fingers will be described hereinafter . as shown in fig4 a retainer nut 44 includes a body portion 46 which is hollow and has a radially outwardly extending flange 48 at a first end 50 thereof . the internal surface of the body 46 has threads 56 formed therealong for attachment to the threaded spindle 14 of the power tool . the nut 44 is inserted through the aperture 26 in the grinding wheel and the aperture 30 in the flange 28 from the front surface 20 toward the rear surface 18 of the grinding wheel 10 . the end 52 of the nut 44 extends through the opening 30 in the flange 28 . the nut 44 is preferably constructed from an aluminum extrusion which is then machined to provide the flange 38 and the threads 46 . alternatively the nut may be formed from aluminum or steel bar stock , or a metal die casting , or molded plastic . once the nut 44 has been inserted through the openings in the wheel 10 and the flange 28 , the end 52 thereof is upset such as by a staking operation to provide a protrusion 56 extendinq outwardly therefrom as shown specifically in fig5 . the protrusion may be formed as a series of separate protrusions , or , as shown , as a continuous protrusion . preferably the protrusion is formed by a staking operation which forms a continuous groove 54 in the end of 52 of the nut 44 . formation of the groove 54 causes the displaced material to form a lip or overhang 57 which will overlie the back of the backing flange 28 about the opening 30 therethrough . it should become apparent to those skilled in the art that the flange 28 and the nut 44 are secured together on the wheel 10 between the flange 48 and the overhang 57 without the use of adhesives . to provide proper operational compressive forces of the throwaway grinding wheel as above - described , a pressure cap 60 is rotated into locking engagement with the hub assembly 12 . the pressure cap 60 includes a first or rear surface 62 for engaging a surface 64 on the power tool spindle when the grinding wheel is in an operable position on the power tool 16 . a second or front surface 66 on the pressure cap 60 contacts the top of the continuous rib 34 . the pressure cap 60 is retained in position on the hub assembly 12 by a plurality of radially outwardly extending tangs 68 , 70 , 72 and 74 . these tangs extend outwardly from a surface 70 on the body 76 of the pressure cap 60 . the surface 70 is defined by a circular wall 78 which is connected to the rear surface 62 by a plurality of radial walls 80 . as is more easily seen in fig8 each of the tangs 68 through 74 includes a wedge shaped portion 82 with the thinner section 84 thereof at the leading edge . a surface 86 defines an inclined plane or ramp which is used in securing the pressure cap 60 on the flange 28 . adjacent the thickest portion 88 of the wedge shaped portion 82 is a stop member 90 . the stop member 90 defines a detent 92 . once the flange 28 and the retaining nut 44 are secured upon the wheel 10 the pressure cap 60 is secured thereon in the following manner : tangs 68 through 74 are positioned between fingers 35 through 41 with the surface 66 engaging the rib 34 . the cap 60 is then rotated clockwise so that the leading edge 84 of the tangs enters the spaces 100 through 106 . rotation is continued to effect an interference fit between the ramp 86 and the finger associated therewith . finally , the distal end 92 through 98 of the fingers will be positioned within the detent 92 of its respective stop member as more specifically shown in fig9 . it will be noted particularly in fig1 that the reinforcing rib 34 has a predetermined radius of curvature and that the surface 66 of the pressure cap has a complimentary radius of curvature . thus , when the two are brought into engagement and secured together , forces are easily transmitted through the body 76 . from the drawings , it is noted that there are an equal number of fingers and tangs and that they are equiangularly spaced . although such an arrangement will usually be preferred , it must be understood that it is not necessary . for example , there may be a greater or lesser number of tangs and fingers and they need not be equiangularly disposed . it should be recognized that the sole function of the tangs and fingers is to secure the pressure cap to the flange . once secured , the tangs and fingers do not transmit or carry loads of any kind . the body 76 of the pressure cap 60 defines an aperture 110 for receiving the spindle 14 of the power tool . when assembled on the backing flange 28 the apertures 26 30 and 110 are aligned axially . as will be noted , when the grinding wheel is in use on the power tool compressive forces are transmitted through the body 76 of the pressure cap 60 between the surfaces 62 and 66 . the bulk of the body 76 between surfaces 62 and 66 and the stiffening ribs or radial walls 80 carry these forces . preferably the pressure cap 60 is constructed of molded plastic such as polypropylene , nylon , acetal or the like . the force necessary to cause the grinding wheel 10 to be placed in compression is generated upon attachment of the spindle 14 to the threads 56 in the nut 44 . by reference to fig1 it will be noted that when the grinding wheel is threaded upon the spindle 14 the surface 62 engages the spindle seat 64 . the interengagement between the threads 14 and 56 of the spindle and nut , respectively , urge the nut upward toward the flange 28 as the wheel is seated upon the spindle . at the same time , the spindle seat 64 applies a downward force to surface 62 of the pressure cap 60 which in turn , through the surface 66 applies a downward force to the flange 28 . therefore , this mutual clamping force causes the grinding wheel to be placed in compression . those skilled in the art will recognize that as the grinding wheel 10 is used by being placed against a workpiece , additional torque is applied causing the grinding wheel to be further tightened onto the spindle 14 . that is , as the grinding wheel moves during contact with a workpiece , the friction between the nut and the grinding wheel center causes the nut to rotate in a further tightening direction . such rotation of the nut further urges the nut toward the flange which in turn applies a further force to the flange . the more the grinding wheel is tightened the greater the operational compression force becomes and the more securely the grinding wheel 10 is clamped between the backing flange 28 and the flange 48 on the nut 44 . as a result of this strong clamping or compression the grinding wheel 10 is precluded from movement relative to the hub or driving member 12 and at the same time is precluded from disengaging from the spindle 14 . however , through the use of the plastic pressure cap the wheel easily releases from the power tool with hand force only when rotated in the opposite direction . it will be recognized by those skilled in the art that the grinding wheel assembly as illustrated in fig1 through 9 and as above described require no adhesive for construction and may be simply and easily assembled , is relatively light in weight as compared to the prior art devices utilizing the cast hubs and provides a secure attachment of the finishing article to the power tool and through the utilization of the increased compression precludes relative rotation of the finishing article with respect to the driving member . it has also been discovered that the utilization of the device as above described and as constructed in the preferred embodiment is extremely smooth in operation with no vibration . the reason for such extremely smooth operation is that all of the parts are perfectly aligned one with the other with the abutting surfaces parallel when in compression and only the wheel 10 can cause any vibration and then only if it is not properly balanced during the construction thereof . through the structure as illustrated and described , all currently known sizes of standard diameter depressed center grinding wheels , namely four inch , four and one half inch , five inch , seven inch and nine inch may be accommodated . at the present time , through the utilization of the die - cast integral hub - flange structure , only seven and nine inch grinding wheels utilize the throw away hub while the four , four and one half and five inch wheel utilize the conventional two - piece mounting set traditional in the prior art and as above described . there has thus been disclosed a disposable finishing article driving member assembly which securely holds the article during operation , which is light in weight , vibration - free , and less expensive than prior art throw - away articles while meeting all safety standards currently known and in existence .