3M™ Flame Resistant Hook Fastener SJ3419FR is our flame resistant fastener with no adhesive or liner. It is an attachment alternative to a wide variety of closures, including zippers, screws, snaps, hooks and more. This fastener is covered with flexible J-shaped hooks, about 300 hooks per square inch (46 hooks/square cm.), which protrude up from a woven backing. This fastener should be paired with 3M™ Flame Resistant Loop Fastener SJ3418FR. To ensure stability and flatness, both the hook and the corresponding loop are preshrunk.