Consider a cover $($otherwise known as "hub cap"$)$ for wheels of passenger automobiles. Sheet metal is pressed to make a decorative cover to hide nuts that hold the rim of the wheel assembly on to the car. The design is simple. Holes are punched in the rim of the wheel and metallic clip springs are welded on the wheel cover. To attach the cover on the rim, the springs welded on the cover are pushed into the holes in the rim, which deflect and snap in the holes. The interference between the spring and the hole keeps the cover attached to the rim. To prevent the rim from falling off the rim when the car goes over a bump and at the same time to make the mounting of the rim easy when fires are replaced by drivers, tests showed that the force for retention and installation must be $34$ N $+/-4$ N$.$ That is$,$ the design range is from $30$N to $38$ N$.$ However, due to slight misplacement of the spring during welding and the wear of punching dies during the fabrication of the rim, it was found that the force is not always in this range. Figure a shows the force distribution