3M(TM) Dual Lock(TM) Reclosable Fastener SJ3440 is black, with 250 stems per square inch and an engaged thickness of 4.0 mm. 3M(TM) Dual Lock(TM) Reclosable Fastener SJ3440 is plain backed with no adhesive. 3M(TM) Dual Lock(TM) Reclosable Fasteners have been used extensively in transportation, electronics, business equipment, machinery, medical and sign and display markets. When the mushroom-shaped stems interlock, tensile strength is high enough to replace mechanical fasteners