its multi ribbed. No you don't really need a tensioner tool just feel the belt before you take it off and try to match it when you put it on. Another thing is since the adjuster bolt has been there for a while the rest of the bolt has aged so once you loosen it tighten close to where the shiny metal of the bolt is about to end and check it. It doesn't have to be too tight because its just running the P/S.