Hello, i have been trying to do the following:

im gonna have several beams as example of "a" and "b", around 200 some in parallel while forming a square matrix.

Because my computer is awful, and it cannot handle too many individual pieces (not even in matrix copy, i tried), i want to add them into a 3d sketch as a sole member.

now see that hole on "a"? i want that replicated on channel "b" , i made it with a simple extrude function up to where the  surface ends, it doesnt go all the way trough, only the top side.

is there a way to this? such an intermittent extruded cut function (where it would skip the bottom half) that i am not aware of, all i could think was to copy the same hole on the other channel and repeat another extrude function but that sounds borderline, any suggestions?, again the main reason to not make it once and insert it into an assembly its because its going to repeat a lot of times, or at least enough for my computer to explode.

if you need additional details of my intentions ask me, thanks!