3M™ Dual Lock™ Reclosable Fastener SJ3871, Black, 1 in x 45 yd, Type 400, 2 Roll/Case. The 3M™ Dual Lock™ Reclosable Fastener SJ3871 has a modified acrylic adhesive on the back of a black polypropylene reclosable fastener. This product can be used both indoors and outside in a variety of applications; and has a slim 0.24” engaged thickness and long service life.