The plaintiff, Rock-Ola Manufacturing Corporation (“Rock-Ola”), brought this action for declaratory judgment pursuant to 28 U.S.C. §§ 2201 and 2202, seeking a declaration of the invalidity of defendant Paul Cusano’s patent (No. 2,479,477) and non-infringement by Rock-Ola’s device, together with injunctive relief and damages for unfair competition. 1 The defendant Cusano filed his counterclaim, based upon the validity of his patent and infringement by Rock-Ola’s device, and in this counterclaim was joined by the American Shuffleboard Company. 2

The District Court, upon findings of fact, concluded that Cusano’s device lacked invention over the prior art. 1952, 106 F. Supp. 723. Cusano appealed, at our No. 10,889. Rock-Ola filed a cross-appeal, at our No. 10,879, asserting non-infringement, and invalidity of Cusano’s patent because of amendments without supplemental oath broadening the claim after adverse rights of-plaintiff intervened. Neither of the issues raised by Rock-Ola in its cross-appeal was reached by the District Court.

The issue upon which we dispose of the entire controversy between the parties is whether Cusano’s device is the product of that imaginative ingenuity which is deservedly rewarded with the monopoly of letters patent. To hold that it is, we should be obliged to reach the conclusion that the findings of the District Court are “clearly erroneous”, and without adequate support in the record. Graver Tank & Mfg. Co., Inc. v. Linde Air Products Co., 1949, 336 U.S. 271, 274-275, 69 S.Ct. 535, 93 L.Ed. 672. Not only are we unable to declare such error or inadequacy, but we are in full agreement with the findings and conclusions of the learned District Judge.

Cusano’s device is a mechanical apparatus for the correction of warpage (due to atmospheric conditions) in game boards, such as shuffleboards. It consists of two T-shaped brackets mounted loosely on the underside of the game board in alignment transversely thereto. The legs of the T’s are connected by a rod, with -a nut on either side of the one leg. By adjusting the nuts, the brackets may be forced apart or drawn together. If drawn together, the inner ends of the brackets push upward and the outer ends pull downward, thus tending to correct a concave warpage. If forced apart, the outer ends of the brackets push upward, and the inner ends pull downward, thus tending to correct a convex warpage.

Cusano does not claim to be the first to provide means for correcting warpage or leveling of game boards, and the claims of his patent admittedly do not define a principle of operation. Rather, it is asserted that the claims set forth specific structural details, not disclosed by the prior art, which enable the device to act uniformly across the width of the shuffleboard to correct convex or concave warpage, and to *553 permit lateral expansion and contraction of the hoard without hindrance.

More, however, is required for patentability than a change, no matter how m~provnig, in the structural details diselos-~ ed by the prior art, Pyrene Mig. Co. v. Urquhart, 3 Cir., 1949, 175 F.2d 408, 410, certiorari denied 338 U.S. 826, 70 S.Ct. 73, 94 L.Ed. 502, Indeed, it is a well-worn rule of patent law, that mechanical skill is not alone sufficient to convert an improvement, where operating principles are retained, into a patentahie invention. Mandel Bros., Inc. v. Wallace, 1948, 335 US. 291, 69 S.Ct. 73, 93 L.Ed. 12; Sinclair & Carroll Oil Co., Inc. v. Interchemical Corp., 1945, 325 U.S. 327, 65 S.Ct. 1143, 89 LEd. 1644.

In the ins~aist case, two prior patents, that of Consp~on (No. 1,677,707) and Bnrrowos (No. 1,001,151) disclose the operatmg principle of Cusano’s device. Both showed a device which was attached to the underside of a game board along virtually its full wicnli. Bun owes showed a 1- shaped biacket^ approximately the same veiacal elongation as Cúsanos blackens. Both showed the use of a rod or Dolt to achieve the movement of the brackets.

Cusano commenced his investigation of the problem, insofar as we arc here concerned, with an adaptation of the Compton device, with which lie was familiar. This adaptation consisted of the use of two L-shaped bars of meiaJ attached across the width of the underside of the shuffleboard and connected by a bolt, which was threaded through the leg's of the L.’s. Depending upon the direction in which the bolt was turned, the 1,rackets were pulled together or forced apart. Cusano said he could casfly see this device would not work on the stiff, massive, strong surface of a shuffleboard top because of inadequate pressure. 3 He attained the desired pressure through the ordinary principle of leverage, elongatmg the legs of the L’s, and in so doing he also recognized the need for a strongly reinforced leg. It was also apparent to him that the desired result was not achieved because the flexing was confined to the very narrow space between the two brackets. 4 And when lie increased the pressure in order to flex tim board, it split The answer was to separate tbe brackets by widening the space between them, to allow a greater distfibntion of the pressure. By so widening the space and redncing the Size of bracket attached to the underside of the board, be also freed that portion of the hoard to allow greater lateral expansion. We agree with the District Court, that this is all lie accomplished when he separated the brackets and put them in hangers. The principle of the resulting push-pull force perpendicular to the board is the same with the hangers in brackets as that shown by Comptori and Bnrrowes, and this is the most important single purpose of the apparatus. The placing of brackets in hangers is not new, nor does it in this device operate in any way different from other brackets in hangers. The tolerance for lateral expansion of lhe board when the device is llot in USft> gained by fitting the banger loosely to the bracket is, we think, incidental in effect. In any event, it certainly does not attain the dignity of imagilla|;ve invention, but rests at the level of routinc mechanical skill, as does the remainder of the device. See Great A. & P. Tea Co. v. Supermarket Equipment Corp., 1950, 340 U.S. 147, 71 S.Ct. 127, 95 L.Ed. 162; Cuno Engineering Corp. v. Automatic Devices Corp., 1941, 314 U.S. 84, 62 S.Ct. 37, 86 L.Ed. 58, as well as those cases already cited,

Cusano relles upon comm««aI success> and tIle fal1ure oi his competitors to deveIop a device slmilar to his in the iace of a need tllercfor- However, as we un¿«stand the law, such arguments, if true, smooth over a doubt> but can íbft ®ap ciealcd by tbe absence of invontive £enius. Jungerson v. Ostby & Barton Co. 1949, 335 U.S. 560, 69 S.Ct 269, 93 L.Ed. 235.

Finally, we agree with the District Court that the determination of lack of invention in Cusano’s device renders it unnecessary to consider the issues raised in Rock-Ola’s *554 appeal. Measurements Corp. v. Ferris Instrument Corp., 3 Cir., 1947, 159 F.2d 590, 592.

For the reasons stated, the judgment of the District Court will be affirmed.