Specially-formulated for superior grinding performance on aluminum. AL-tra cuts improve grinding on aluminum 400 – 800%. These revolutionary discs resist loading, ensure higher cut rates, prolong disc life and achieve a superior finish. AL-tra cut discs replace conventional resin fiber discs 5 to 1 or more. Back Up Pads for Blending Discs;Compatible with Norton Speed-Lok® Back-Up Pads.