I was looking at pictures of the F18  (very nice!)


There is a bolt/screw on the back of the box at the top and bottom.    What is the function of these?
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Oh!   Never mind, I'm fairly certain I just found the answer:

Since the F18 can be stacked more than 2 tall, and we do have customers in earthquake prone regions, we have included 2 3/8-16" threaded inserts at the top and bottom rear of the cabinet. We will soon be offering a rectangular locking plate which will secure the 2 cabinets physically to guarantee they cannot move separately, and even allows the top most insert to be used as an earthquake restraint/anchor. Here is another look at the rear of the cabinet where you can see the 2 large flat head, 3/8" screws which are flush with the box but can be used to secure the units together:
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Good hunting Dave.

For most cases, the fact that the drivers are all moving in unison means there is very little force wanting to move the subs separately, and instead they move all together.  In locations where earthquakes are an issue or any worry of someone or something giving the stack a hard bump, the big 3/8" threaded inserts give us options to secure things further.
Mark Seaton
Seaton Sound, Inc.
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