Veritas, a small German maker of rubber and plastics products, led the supplier index with a return of 81.3 percent in the second quarter.
The family-owned company also achieved the top return over the past three years, paying back 531.4 percent to shareholders in the three-year period ending June 30.
The second-best performer in the quarter was Labinal, the French aeronautics and auto equipment maker.
Steve Utting of PricewaterhouseCoopers said Labinal's 55.4 percent return reflected its acquisition in May by Snecma, the French state-owned aero engine maker. Labinal's automotive operations, which specialize in making switches, sensors and wiring have since been sold to Valeo.
Fiat-controlled Magneti Marelli was the top performer in the one-year period ending June 30. Magneti Marelli achieved a one-year return of 116.4 percent. The supplier has benefited from several moves, including a lighting joint venture with Bosch and the sale of some minor businesses.
The company has expanded into retail repair through the acquisition of the European and South American operations of Midas repair shops.
Marelli also benefited from the premium price paid by Fiat to buy back shares. The buyback was announced in May.