Hello @wendy.huang2
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The difference in part number 19-SJ3551CF-ND and part number 19-SJ3551CF3M1-ND is going to be the width
part number 19-SJ3551CF-ND is a 1/2" wide, whereas part number part number 19-SJ3551CF3M1-ND is 3/4" wide
you can find the information for the difference on 3M website
3M™ Dual Lock™ Reclosable Fastener SJ3551CF, Black, 1/2 in x 50 yd, Type 400, 4 Roll/Case | 3M United States
3M™ Dual Lock™ Reclosable Fastener SJ3551CF, Black, 3/4 in x 50 yd, Type 400, 2 Rolls/Case | 3M United States