Snap-On Inc. said it would pay $44 million to a rival, the SPX Corporation, after a federal arbitrator decided it had improperly used SPX's patented technology for equipment that tests car engines. Snap-On, which makes tools for the automotive maintenance industry, said it would set aside $27.9 million, or 48 cents a share, against fourth-quarter earnings to pay the after-tax cost of the arbitration award. The dispute started in 1996, when Snap-On, which is based in Pleasant Prairie, Wis., accused SPX of infringing its patents and improperly hiring away an executive from the Sun Electric Corporation, a company that Snap-On bought in 1992. SPX, of Muskegon, Mich., countersued, accusing Snap-On of infringing on its patents.