Stems in wave pattern, approximately 250 stems per inch.
Type 170
Wide rows, approximately 170 stems per inch.
Type 400
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.