3M Scotch-Weld urethane adhesive 640 is a two-part, non-sag urethane adhesive. This adhesive features non-sag and shear thinning properties that allow for accurate and precise application. - 3M Scotch-Weld urethane adhesive 640 delivers tough, flexible bonds with good adhesion to a wide variety of substrates, especially wood and many properly abraded and cleaned plastics.