Stems in wave pattern, approximately 250 stems per inch.
Wide rows, approximately 170 stems per inch.
Heads almost touching, approximately 400 stems per inch.
Stem count combinations:
250 to 250: Recommended that you use the 250/250 as it simplifies assembly processes. This is by far the most common closure combination, and is the solution for nearly every application requiring dual lock. It is a very specific applications that require a different stem count combination.
170 to 400: Same closure strength as the 250/250. Originally dual lock was made in only this combination. 3M created the 250 stem count which eliminated the need for this combination.
170 to 250: This will give you little extra fastening strength vs hook & loop ("Velcro"), but noticeably less than a 250/250 combination
400 to 250: This will give you some extra grip beyond the 250/250. There should be an expectation of a reduction in cycle life with this combination.
400 to 400: Not recommended by 3M, but we do have customers that use it though. Expect to have a difficult time fully engaging this combination, and have something handy to help pry this apart when you want to disengage. Cycle life is drastically reduced in the 400/400 combination to as few as 3 or 4 cycles. It is possible after one cycle to rip stems out.
170 to 170: Not recommended by 3M. The stems are too far apart and will slide causing the application to fail. We have never seen a functioning application for this combination.