Museo Alu-Frame Aluminum Stretcher Bars feature a reinforced structure comprised of wear-resistant aluminum and sturdy wood for maximum stability. Unlike all-wood stretcher bars, aluminum bars are unaffected by changes in humidity and temperature. They won't twist, bend, or warp. - MUSEO ALU-Frame Aluminum Stretcher Bars and Parts - Corner Stabilizers, Pkg of 8Museo Aluminum Stretch Bar, SET 4 - These pieces add strength to the corners of larger frames and are recommended for works bigger than 72" × 72" and for 60" × 80" or 48" × 96" frames. Sold in a pack of eight (two for each corner).